I'm sure you're probably right about video games being used in training and, as a result, the models reflecting video game physics: No air resistance, no static/dynamic friction curve, etc.

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.

Yes this is right. Something about the way it works under the hood means it wants: 1. bust falls 2. it crushes the watermelon 3. it teeters 4. it settles on the plinth. It is sort of interpolating between these states, which it feels are a realistic sequence of events, not actually attempting to model what would happen in a real "world".