PS3 won't show more than a certain number of characters on-screen, so crowded areas and boss fights aren't a problem. PS3 can also easily handle the polycount of the characters and world, textures are a bit lower quality due to lack of (V)RAM.

There are plenty other optimisations that can be done, and Squenix has EXTENSIVE experience with making games look better and run smoother than what people expected from a console.

And like others have said, don't underestimate what optimisation can do for a game. I've seen games go from nearly unplayable to very enjoyable after 1 person (specialised in optimising 3d engines) tweaked the engine for 2 weeks.