But how can a layman know where the line is for a particular use? The uncertainty itself has a chilling effect on creativity.

Asimov wrote:

The world in general disapproves of creativity

We can see evidence of this in how copyright treats derivative works. All works build on other works, as Asimov wrote when he described connecting A to B to C, yet some forms of such building are forbidden by law.

My point is that Debian and Debian-derived distributions let the owner of a machine edit sources.list and Android doesn't.

Ask users of Snapchat.

At least Lexmark v. Static Control Components, the case I assume you're referring to, was decided in favor of interoperability.

Any application that requires Windows XP Mode, SUA, or more than 16 GB of RAM will work only on Windows 7 Pro and Ultimate according to this table. So does any application that is accessed remotely through Remote Desktop.

If the malware didn't need root to enable itself as a device admin, then you don't need root to disable it. Most Android malware that makes the news is not the alleged "malware" installed by carriers, and besides, that's easily avoidable by buying Nexus or Google Play Edition devices and avoiding VZW and Sprint.

Canonical put time and effort into the Personal Package Archive system, which supports competitors to the official Ubuntu repository. Each PPA is a Debian repository with a public key to verify packages, and a Canonical-managed PKI ties them together. True, a lot of that comes from the Debian project, but Canonical still polished it into PPAs starting in Ubuntu 9.10.

Yet because Apple rejects useful applications such as MozStumbler and any web browser that isn't a Safari wrapper, users end up having to deal with a platform that allows use of unsigned binaries without payment of a recurring fee to the operating system publisher. They have nothing to do with each other technically and everything to do with each other politically.

Then what's the point of Google Play Store, Amazon Appstore, and F-Droid, which all have a sizable collection of apps available without charge? In F-Droid's case, the apps are even free software.

Is it really any different from ways to pay for purchases on Windows Phone Store?

You could always install Classic Shell, an aftermarket launcher for Windows, to put the S back in Window 8.1 and give you an interface that's closer to Windows 7. Android likewise has aftermarket launchers.

Which is like installing a custom ROM on an Android device: there's ABSOLUTELY NO WARRANTY that all peripherals will be supported. I still haven't got my laptop's Bluetooth working in Xubuntu.

And ARM vs. MIPS vs. Atom.

That's more a matter of which OS component repositories you're allowed to access than actual OS fragmentation.

I read Anonymous Coward's comment as complaining that Windows, X11 desktop environments, and Android have the "associate the file format with the viewer" feature in the first place. AC wants the user to have to remember the name of the viewer.

Because not all images are single-layer PNG or JPEG. There exist a lot of image formats a viewer for which is not included with all major operating systems. Compare to a common tactic used by Windows trojans: a web site displays a video with an "unsupported codec" and then ships the trojan disguised as a codec installer. Does Windows even come with a PDF viewer?

Even if you carry an iPhone or iPad as your primary device to avoid trojans, you still have to carry an Android device if you want to use legitimate applications that belong to entire categories that Apple is known to reject.