ATI says its R520 and R580 GPUs are also capable of doing heavy physics calculations:
Both ATI and NVIDIA are using the same method of computing physics on their GPUs -- load and process some physics calculations if there's just one GPU, or load and process all physics calculations onto one full GPU if there are two GPUs (Crossfire or SLI). In regards to both methods, the approach is monolithic, meaning that both ATI and NVIDIA prefer to load all things related to graphics onto the GPU. ATI claims that its latest X1900 family has more than enough processing power left sitting idle most of the time to take care of physics and 3D rendering. This is a strong indication that the current state of 3D graphics is far too concerned with frame rate when it should be looking into how best to utilize the chips that ATI and NVIDIA produce.