The game is heavily scripted in a way and that is in the fact that it chooses from a library of animations and streams them off the disc instead of actually doing a 3d simulation of your character including the body, muscles, motor system, and surrounding environment like what Euphoria does for example.
It's also one of the reasons why The Last of Us and the Uncharted series look better than most games. Basically Naughty Dog is saving some CPU resources by faking a true 3d simulation of the environment while other games like Red Dead Redemption that use Euphoria don't. That and they can add more detail to the canned animations.
The drawbacks to their solution is that it can leads to a lot more disc space being taken up (not a problem with linear games the size of Uncharted, The Last of Us, and God of War 3 - and Sony using Blu-Ray), being too cost prohibitive to implement in a larger open world game, and having scenes play out in almost the same way if a person happens to trigger many of the same animations like in this case.
Many people seem to think these games look so good because of the PS3's processor, that actually isn't true at all. The reason is because Sony chose to use Blu-Ray discs. If Microsoft had chosen a similar large format they could have made games using similar methods and may have looked even better given the 360's architecture.
