They don't change physics or anything. CUDA support has been in nVidia drivers for the 8-series cards and higher for a
very long time. Nothing uses CUDA at the moment, so it won't change anything.
You may be thinking of the new PhysX support, though. Since nVidia acquired Ageia, they rewrote the drivers to work with CUDA. The only benefit to this is that you can now enable PhysX support in the 4 or 5 games that actually support it.