well for xbox 2 i could see an amd processor since it would prolly use the inbetween 1ghz to 2ghz range and the p4's in there just suck massive elephant dick, or ms could do something interesting and invest in a custom built cpu thats better built to handle the stuff a console does(lower heat dissipation, less power consumption) instead of just having a highly customed pc.
oh and does this mean since the p3 is just plain jane p3 that you could swap in a faster model so it would run a bit faster and cooler. nothing like having a house thats inside temp is around 36'c to make you fiddle with slowing down the cpu to keep it from frying itself.
also i realize the clockspeed might be locked to 733 but a processor thats designed to run faster would give it some performance boost. learned this when i had to fix an acer and i popped in a 166 in place of the 133 and the stupid thing was locked to 133 but the performance went up. maybe its just that its the core is better designed so the electrical impulses fly around better.