Over the course of the years, games have been growing progressively more complex. While we were happy with vertex enemies back in the 90s and regular textures were enough to please us at the break of the new millennium, we immediately mark a game as ugly and last-gen if some sort of advanced lighting or pixel shading is not in effect today.
Similarly, nobody complained when shooting an explosive barrel in Quake 2 only killed a nearby enemy, but today its body must not only get thrown into the air realistically, but the body must behave as a real world object would in the given situation. Gamers even look for more complex physics body interactions such as the impact a box has on other objects when thrown at them. If you take a look at the upcoming Force Unleashed trailers you will see that things are moving forward at blazing speeds and as a result only the fastest CPUs can be sure of handling the increased load.
The graphics industry faced a similar situation back in the days of 3dfx, when something had to be done to offload some of the work from the CPU and allow games to develop. Back then 3D acceleration was introduced and right now AGEIA is trying to do the same for the world of physics.
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