But Nvidia isn't in the physics business, they're in the GPU business and so far it seems their goal for physX is to leverage their GPU sales not more nor less.It doesn't make logical sense to be in the Physic business and to ignore the CPU. Physx is a multi-platform, device, engine, library and tool set, and so much more than just GPU physics.
You may disagree with that (because there are a whole lot of reasons why it's bad for gaming as a whole), but it makes sense for them and developing a SSE/AVX version of physx wouldn't help them much from a business perspective (and cost a considerable amount of money, it's not just changing a compile switch like some seem to believe), so I doubt we'll see much engagement there.
But hey there are other libraries out there as well and we can at least hope that physX keeps other vendors (Intel, AMD/Ati) on their toes to do more about them. The future of physics on the PC hopefully won't be physX, but it surely will affect the field.