First, their Mac line will still run Intel CPUs, while the iOS line runs ARM based processors. You can't really merge the two for various reasons.
While another individual responded to this better, the point of being a "functional" difference in the context in which I was suggesting it could be better defined as "related to the end user experience independent of GUI-explicit elements". Most end users would believe Tim Cook when he says "It's fast", and that would basically be that (as long as they delivered, of course).
Second, the Macs are "open" devices, while the iPad is a walled garden. This is a fundamental problem that cannot be simply washed away. Either you run x86 binaries on iPad freely, or you run walled garden apps on yoru Mac.
What I was effectively getting at was that the Apple platform is indeed headed to walled garden apps. Now by "walled garden apps" I do also include things like Maya and Logic Pro and Aperture, not merely Angry Birds and Pixlr...but "walled garden" just the same.
Don't underestimate the implications of the second point - it would mean either the iPad runs applications under emulation but unsigned, or the Mac runs signed iPad apps. The latter doesn't accomplish much, while the former is a pretty huge thing (you can get around the App Store).
Why couldn't applications be both signed and emulated? Why couldn't a theoretical Macbook Air include an A7 processor to run iPad apps? Why couldn't Apple include an "auto recompile" in the SDK to allow developers to make an iPad app that will run on a MacBook Air? I don't pretend to be anything but ignorant in this regard, the point I'm grasping at is that I can't imagine Tim Cook saying, "you could run PowerPC programs on Intel chips that were half as powerful as what's running the current crop of iPhones, but running Temple Run on today's x86 chips is impractical? aww shucks, that's a real bummer."
There is no way Apple can really lock down the Mac platform, either - when jailbreaking is as simple as taking out the SSD and modifying the contents on a different machine.
1.) Because "taking out the SSD" means "prying open the unit and desoldering".
2.) Because even if it didn't, there are things called "Secure Boot" and "Signed Bootloaders" that seems to be pretty good at making a mess of things when it can't be disabled.
And there's enough software out there that losing compatibility with OS X is not an option, either.
There's enough Firewire based hardware to make a whole lot of film and music professionals pissed at Apple; between a $2,000 Macbook and a $10,000 video camera, which do you think is getting the boot? "It depends" is the correct answer, and for some, the Mac platform was the one to get shown the door. I'm not saying that future Macs will be utterly incapable of running anything but iPad apps, but I am saying that I don't see Apple remaining open "because Slashdot thinks it's a good idea". Better example: Rosetta emulation. There were plenty of incredibly expensive pieces of software that were written for the platform, but after a very long time, Apple deprecated it. what gave Apple the ability to do this was to provide an alternative path, wait until the overwhelming majority of high ticket software vendors had a release or two that supported Intel natively, then remove Rosetta going forward. This allows for "steps" - first, the writing is on the wall so that users can eyeball upgrades. Next, users can still use their existing hardware and OS releases, but as clock speeds and RAM amounts tick up, the performance of the aging machine along with the availability of new releases of the software makes it a "good idea" to get all the new features and better performance. By time Rosetta was deprecated, it wasn't missed enough to cause a revolt.
And the default option is to allow signed (but not app-store) apps and app store apps. Because there's still a large contingent of software used on Macs NOT sold in the MAS. Little known titles like say, Microsoft Office, Adobe Photoshop and others.
The default option FOR NOW is to allow signed apps, because FOR NOW, Office and Photoshop aren't in the Mac App Store. With Adobe headed to the Creative Cloud model (and Microsoft trying the same thing with Office365), I see it as only a matter of time before "Creative Cloud Installer" and "Office 365 Installer" end up in the MAS. Against the rules? For now it might be, but for worse or even worse, Apple and Adobe have had a rather symbiotic relationship (and to a much lesser extent, Microsoft - Office is still one of the best selling pieces of software on the platform and Apple advertises its availability prominently). Once those and several others end up in the MAS, then anyone NOT in the MAS becomes a second class citizen, since it's foolish to Google software for the Mac when the MAS has everything you want and it's just a matter of filtering it. By time the ability to install unsigned applications comes along, the Rosetta situation will repeat itself all over again.
Plus, there are enough things that cannot be done in the MAS isolation model that people expect - plugins, for example are impossible under MAS (And never get between a musician and their plugins!). As are device drivers for hardware.
You raise an interesting point with device drivers, though Apple has generally been plug-and-play for basically everything; it's the increasingly rare and exotic piece of hardware that requires a Mac driver that it doesn't have or pull from the internet automatically. Regarding musicians and plugins, believe me, I know the drill, as I've got more than a few friends with Waves and Izotope bundles that cost a fortune. This might be the best argument you've made, but two counterpoints spring to mind: first, once again I can't see Tim Cook being willing to forego the 30% cut of plugin suites that cost thousands of dollars on account of there being a dearth of low-level system access from within the sandbox. What I can almost see happening as a quick example would be a situation where the people who say they need that kind of access would have to submit full source code for analysis, at which point they get a "super duper" badge and can have a special low-level system access mode. Maybe it will turn out completely differently, including you being right, but I don't see that kind of problem as an insurmountable obstacle for Cook and company. My second thought is that Apple has seemed to be consistently preferring the consumer over the professional for some time now. They let the Mac Pro rot for years as even econobox workstations were outspeccing them, then when they update it, they make it so that every peripheral must be external, including hard disks. Apple wants consumer dollars for good reason, and the Mac Pro was a slap in the face to the NLE/DAW/CAD/DTP customers who had consistently preferred the company for years. Would Apple get between musicians and their plugins? Well, Apple got between video editors and their internal hard drives. They also got between video editors and their DVD burners, while never once offering an internal Blu-Ray authoring solution (more on that in a bit)...so I can't put it past them. Bonus argument: There's quite the cottage industry of musical peripherals for the iPad now; you can find plenty of Youtube videos of people doing all kinds of musical awesomeness directly from their iPad.
And gatekeeper is more subtle than that - you can run unsigned apps that did not originate from the Internet (it's an extended attribute that gets set) without a warning - the presumption is that it was obtained from "trusted" media - either the output of a compiler (hey Open Source - what better way than to enforce compliance than by only allowing source code distribution?), or through a CD or DVD back in the days.
Once again...for now. I'm not saying that Apple is hostile to third party software distribution NOW. I'm saying that 5-6 years from now, they have all the incentive in the world to become that. Bonus nugget here: Why doesn't anything from Apple come with an optical drive anymore? Yes, they have plenty of USB optical drives for sale with your Mac, and I know that plenty of people just use USB storage or Dropbox, Apple loves saying "it's thinner", and how everyone and their cousin does video via Youtube now. However, the most expensive DVD most people will ever buy is their wedding video. No bride has ever wanted to be delivered a Vimeo URL, they still want a tangible copy of something they easily paid thousands of dollars for. Plenty of the event videographer segment preferred Macs, and still do. Thus, I have trouble believing that there wasn't a market anywhere for a laptop just for them. Hell, IBM made its Thinkpad W700 series, which was a beast of a machine explicitly designed for media pros (well, the pros that were cool with dropping $5,000 on a base model). If this market segment is big enough for IBM to attempt to address, then surely it must also be big enough for Apple to attempt to keep happy...but I digress. Gatekeeper may be subtle, but it went from "nonexistent" to "subtle" - there's a progression there. I question the faith with regards to "subtle" being "enough" for a company that's rearranged chip designs (to say nothing of software rewrites) in order to thwart third party software from installing.
The thing is - Apple cannot change the default setting without harming a lot of users and 3rd party developers. Especially with sandboxing that forces each app to not even be able to get very far outside the filesystem it's limited to.
As has already been extensively covered, the two refrains here are "over time", and "it hasn't stopped them in the past".
...Because MAS apps are sandboxed, even if malware attacks it and infects the iCloud storage, the app remains isolated...
I don't see how this segment disproves what I'm saying, in fact it seems to corroborate it - minimize malware, minimize piracy, make users more dependent on iCloud, show John and Jane Q. Public that Apple even protects you in Teh Cloud(tm)...All of this sounds like the kind of reasons that people would naturally choose MAS applications, which will gradually cause traditional retail and download distribution channels to dry up, and because no one installs anything from Safari anyway (Besides malware and cracked software, of course...), the inability to install unsigned software becomes an issue on Slashdot and enough money flows to Cupertino to buy a new platinum-plated Tesla convertible every day.
But getting a signing cert from Apple lets you bypass the MAS...
...so either you get listed in the MAS (which Apple blesses), or you get a signing cert from Apple (which they inherently bless)...and there's nothing possible that could go wrong there...
... And do things that no sandbox would allow - install drivers, allow access to the entire filesystem, plug into other apps, etc.
It's become more and more bewildering to me how many people don't have the slightest concept of how a file system works anymore, even at a rudimentary level. Access to one is useless for most people, especially if Apple adds something like Android's 'share' API that allows me to 'share' data between apps that can talk to each other. With all of that in place, especially with iCloud managing the strings, it seems like the perfect setup. Installing drivers, once again, only necessary for some really oddball stuff, for which most people would not care. If it really came down to that, I see things going polar - either the hardware is good enough to justify musicians starting to look at Windows machines again (and dear God do I hope that Microsoft start making an actual, non-sucktastic desktop OS available once they start looking), or the hardware manufacturers do some really innovative stuff to make their hardware class compliant.