Gameplay is directly influenced by the "feel" of the world. I am not strictly talking about photo-realism, but (1) how the world reacts to input (2) how is it consistent.

Physics is not about real world accuracy, but about how consistently stuff interacts (and its side effects like illumination) in the virtual world. There will be a time in the future when the physics engine will become the rendering engine, just because there are infinite gameplay possibilities in such a craft.