Sorry, pure guess is wrong.
IBM has a large chip business, and with Cell processor is putting more behind it. They sold PC hardware because it wasnt making good enough margins, and they are now in the business of being a 'technology' supplier to companies liek DELL.
Moreover, Freescale wants to sell chips and would be happy to supply 100% of Apple's needs if IBM didnt want to. (Currently Apple takes Freescale's G4 and IBMs G5). It was an Apple decision, not an IBM/Freescale decision.
The way I see it, it only makes sense in this perspective: If Apple made this decision 20 years ago, we'd have gotten a viable competitor to Microsoft.
Apple must be thinking that their hardware margins are effectively 0%, and they can compete on their software basis. If that is the case, you should be able to but an "OS X" software package and put it on your own PC box.
That *or* they feel the desktop is becoming less and less relevent.
IMHO, this decision is not right - they are missing the boat on the OS wars, and they are also missing the key value differentiator they have in a closed box solution. 20 years ago, this would have been the right decision. Now, when by their own admission the CPU / OS layer is more flexible *and* you have "OS X"-like OS available on x86 ... LINUX ... this is throwing away some real Mac advantages and putting them in direct competition with more low-cost alternatives.
Mac OS X on Intel sounds a lot like Solaris/x86, which ended up going nowhere.
I would find the task of supplying drivers for the diverse number of add-ons for the PC to be daunting, if they go that direction it will be interesting to see how they survive the "your OS doesn't work with my off-brand/legacy video card" crowd.
Actually I am dumping most/all of my Linux servers and going with Solaris/x86 and a smattering of older SPARC machines also running Solaris.