It's something each game developer is looking at at a game by game basis, as everything you do, and the game does uses power, and they can plan their games around that.
I remember reading something with one of the guys who made Ridge Racer for the PSP and was saying to help conserve battery power they clocked the processor down.
It is something that's being addressed, but it does depend on the game and I suppose how lazy the developers are feeling
