However, I don't think that's the problem in the example of the marble bust not toppling. It would have toppled in a video game engine as well; they model gravity and inertia just fine.

I think what's happening is the model isn't being a world model at all, it's being a language model. It's trying to make the "scripted" thing happen, and it probably "feels" like the script should end in the bust on the pedestal.