I'm not sure where you came up with the statement that the Cell’s PPE is derived from the POWER 5, but in your own link to Anandtech's article on the cell it states "The PPE is a new core unlike any other PowerPC core made by IBM."
It is a very simple, in-order execution processor with a high clock speed to help offset this in-order design. If it is derivative of any IBM design, it is certainly not the POWER 5.
For a detailed analysis of the Cell, I recommend Jon "Hannibal" Stokes' articles here:
Part 1: http://arstechnica.com/articles/paedia/cpu/cell-1.ars
Part 2: http://arstechnica.com/articles/paedia/cpu/cell-2.ars
As mentioned by a poster above me, you seem to be downplaying the difficulty of extracting performance from the Cell for general computing tasks. Yes, the Cell is a media processing beast and has the potential to be a boon in certain computing tasks. However, the majority of code run on personal computers (you know, the ones that Toshiba, Sony, and Apple all make) does not benefit at all from the additional SIMD processing elements in the Cell. So the only thing you're left with for day to day computing (web browsing, word processing, chat, email, book keeping, and so on) is the relatively weak processing power provided by the Cell's PPE. Granted, if you wanted to encode one of your DVDs into a format suitable for your Video iPod, the Cell would whip through it like a bulldozer through cheese.
Quite simply, the Cell is not in any way well suited to general purpose computing at all. Yes, it may suffice in that role and under certain conditions, but every application of it deals with processing massive amounts of data: games, scientific and high performance computing (supercomputing), media processing, and other workstation (aka task-specific machines) environments. I'd love to see a Cell co-processor paired with a general purpose CPU. We see such pairings of powerful, highly parallel media processors with general purpose CPUs all the time. They're called video cards. They are great at what they do, but if you tried to run an OS on a graphics chip you’d kill yourself.
I think you're pretty far off the mark to suggest that Apple has to fear the Cell being adopted by computer makers as a central CPU. In fact, I think your argument that Cell-based devices such as a Linux powered PS3 will do anything to impact Apple or Microsoft on the desktop. The Cell is just not designed to be a general purpose CPU, and attempting to argue otherwise misses the point.
However, you are correct that the PS3 is an excellent vehicle to expose a large number of people to Linux.