Not this one again :-)
IMO PPC was chosen because:
* Amiga already uses it
* There are lots of Amiga PPC apps
* It's too easy to get pushed out by windoze on x86
* More custom hardware helps stop piracy
Of course there are other reasons like less heat produced, but those are some of the major ones. Try searching the forums for past threads on this (there are loads :-D)
64 bit doesn't come into it - the PPC970 will be 64 bit, but AOS won't be for a while. And the market is tiny at the moment - anyone who wants to buy one now probably knows what PPC is. That could change later.
Also, remember that both Genesi and A inc chose PPC - they cannot both be wrong... can they?