Some games are only supposed to run at 30 FPS (NTSC versions anyway). Increasing a 30 FPS game to 60 FPS does not increase the quality of the game. Everything will just move 200% faster, and not very fun to play, unless you're doing something like YouTube play-throughs.
Most console games are fixed frame rate games. The motion and animation of onscreen objects is dictated by the frame rate. If the frame rate drops to half-speed, everything moves at half-speed. A lot of PC games have frame rate independent motion, in other words, it doesn't matter what the FPS is. Say I make a character walk in my game. I can specify that the character walks 20 feet in, say 5 seconds, regardless of if the frame rate is 30 or 60 or 1000, as calculations are based on time.
EDIT: ninja'd again, LPFaint...
Most console games are fixed frame rate games. The motion and animation of onscreen objects is dictated by the frame rate. If the frame rate drops to half-speed, everything moves at half-speed. A lot of PC games have frame rate independent motion, in other words, it doesn't matter what the FPS is. Say I make a character walk in my game. I can specify that the character walks 20 feet in, say 5 seconds, regardless of if the frame rate is 30 or 60 or 1000, as calculations are based on time.
EDIT: ninja'd again, LPFaint...