GamesFirst! has published an article entitled "Oblivion's Missing Physics", in which they provide some examples of why Bethesda's The Elder Scrolls IV: Oblivion lacks "casual physics." Here's a bit to get you started:
While Oblivion manages to deliver rag-doll physics, other physical interactions are glossed over. For example, snow effects are merely a mask that covers the screen; your own movement during a snow storm does not effect how quickly or at what angle the snow falls. In other words, the falling snowflakes never get closer to you as you move towards them.
This is done for a simply reason: the amount of processing power required to calculate the physics of each individual snowflake is too great for a system without a dedicated PPU (Physics Processing Unit) to handle. All the system's processing power would be claimed by physics calculations instead of texture rendering, A.I., and game functions.