Can you really say that of the 360 though? It has been the lead platform fo so long and has a standard architecture, so whilst I would say that it's performance has been much better than the ps3 up to now, I couldn't agree that it's potential hasn't already been tapped.
Though, perhaps if the ps3 becomes the lead dev platform, that will indirectly benefit the 360 into the way the games are coded.
By your reckoning then FF12 and God of War on the PS2 shouldn't have looked any better than games that were made 5 years into the PS2's life. What makes you think that after 2 years the whole of the 360s power has been tapped? 6 threaded programming is not a simple task to get right and make efficient and for some bizarre reason you think programming for the 360 is a walk in the park compared to the PS3 when in reality making full use of either system is a complete pain in the ass.