The macbook and iMac will be the next machines to move to a proprietary ARM chipset away from the relatively open X86 platform.
...what on earth has the processor got to do with whether a system is open or not? ARM is supported by Linux and is used in the majority of smartphones and mobile devices - including "open" ones like Android phones and competing "pads". Don't be fooled by the "A4 Custom Chip" thing: since ARM doesn't sell chips but licenses system-on-a-chip component designs on a mix'n'match basis, all ARM implementations are "custom chips". Unless, of course, you have an inside route to Apple and know something we don't about the A4.
Apple cannot stand the fact that the cheapest computer that runs OSX is the Dell Mini 9.
Apple doesn't give a flying fuck about the odd hacker who installs OS X on their Dell Mini, as long as they don't try selling them commercially (sorry, I take it we're just trading bald assertions here, since you're not citing any evidence either).
In other news, ARM do ultra-low power mobile/embedded chips - they haven't designed high performance desktop/high-end laptop chips since some time in the 90s. ARM simply isn't an option for the top end iMacs, MacBook Pros and Mac Pros. The whole reason Apple shifted to x86 (at great expense) in the first place was that IBM/Freescale weren't producing competetive processors fast enough.
Then there's other factors such as continuing support by developes such as Microsoft and Adobe on which the Mac market relies, and the big selling point that Intel Macs can run Windows via dual-boot or virtualization if needed.
Of course, it is possible that Apple could decide to ditch the "proper" PC market and concentrate on "appliances" - but that would mean handing a large section of its customer base over to Microsoft.
You call them appliances all you want but really they are not appliances (akin to a coffee maker, microwave etc) as they are far more complex.
Apple sells shedloads of kit to consumers because Apple understands that consumers want their music players, phones and web browsers to be as easy to use as coffee makers.