The PS3 isn't holding the Xbox back... You got it all wrong... The PS3 may have awesome specs, but the console is so poorly coded, it's harder to make games run faster.
Go on Black Ops on PS3 and Xbox, Split Screen. Have 2 players and get a Gunship or Chopper Gunner in it. The PS3 version lags like crazy, losing lots of frames while the Xbox still goes strong. The PS3 is no way any better then the Sega system.
So if they did have to tone it down for PS3, why does it lose so many frames if they already toned down the game?