Personally, I have never noticed this. Usually the fans on my system continue to increase in speed as the game goes on until they reach either 4k or 6k rpm. It varies a lot depending not only on the game, but the complexity of the level within the game and if I have anything running in the background.
A lot of times I will use smcFanControl and set the fan speeds to 6k just because my MBP gets pretty hot, even with the fans at max speed.