John Carmack is propably one of the most talented programmers out there, sadly he is also one of the most closed minded,he likes x86 and only x86.Since the X-Box is a x86 based console it makes since for him to like it.
A while back he talked about AltiVec implementation in the Mac version of Q3A, he said it was too difficult (when it is known that AltiVec implementation is easier than implementing SSE instructions) and not worth it, some other guy at iD who had more experience with PPC code managed to get it working in a week and it payed off.
I don\'t really trust his word when it comes to consoles,when he\'s talking about PC\'s I belive him.