Garnett said: Actually to be honest,both GPU hit there limits when they came out,now the devs are just making the game AROUND the gpu,and squeezing the last bits out. |
Yes, and no.
As others have said, there's a ton of interactions going on between the GPU and other aspects of hardware. Because of that, there's a ton of optimization between the interactions of the GPU and other parts of the machine:

Think about how much bandwith is being transferred inside the X360 - and how difficult such a beast can be to manage (as it is with any system). Because of that, it'd be like saying about a car "sure, the engine has been finely tuned, there's very little else" - but you have to take everything else into consideration under the hood, as well as everything not in the hood (aerodynamics, body weight, tires, ect).
Since there's so much to be optimized, it's a difficult thing to say 'oh, we've optimized the X360 for this much power' when it's likely there's so much more thats un-tapped. I learned this a lot when I was a mechanic for paintball equipment - if you wanted to fine tune a specific marker, there were dozens of things you could to to make it work great - sure, there was 1 part that was huge, but there was so much more to make it tons better.