Not really. They could focus those resources onto enemy count, large environments, special effects, and probably Titan encounters.
Until we see what GoW3 offers throughout the entire game, it'll be kind of silly to assume why the game should or shouldn't have a certain feature.
It's entirely possible they leave out self-shadowing on grunts because they plan to have scenes where the engine will render dozens of them at one time.
I understand that Self-shadowing looks good, but I really don't see the ridiculous obsession with it. There's nothing wrong with a game that looks good and plays well. Not every game has to look ZOMG on top of playing well. I think having that mind set really robs you of a lot as a gamer.