It is just shadows guys. They explained a while ago the 30fps was for the PS3 "purists" who wanted the game to feel as close to the original. With them limiting it to 30fps, they could up some details that would probably hurt that 60fps mark. This is the way every developer should do it. Give the user an option to play @ 60fps but lose some detail, or play @ 30fps and gain some detail.
I am a PC gamer #1 and the first thing aside from AA that I turn down to gain fps is shadows. They look good sure, but you hardly notice it when enjoying the game and they hit the performance a lot.







