The 480 is no doubt better at certain things such as tessellation and has the added features such as physx, 3d support and CUDA but If I were to spend the cash I would go the 5970 since it is faster at the same price point.
To be completely and utterly fair though, PhysX simply isn't a feature, it's a gimmick they put on their feature list so that people like you say things like you've said.
The same is similar for 3D support as well, it's a feature, but you're not told that it halves your performance
always. You also need an expensive 120Hz monitor, and the glasses aren't cheap either, it's also a gimmick in a sense to the majority of people.
CUDA's all well and good, but again, it's kinda a gimmick (not that's it's not good or useful, but most people playing games aren't interested in features not relevant *okay, Just Cause 2, but that's one out of thousands of games*).
Add all that to the cost of them in the first place and there lies the bulk on the problem. You're looking at £800+ for a GTX480, 120Hz monitor and the 3D Glasses.
I'm not slating 3D, I love it, but I feel it's too expensive and has that one big performance issue.
CUDA too, can be very useful, I'd love to be able to take advantage of its GPU rendering usages, but I know full well that while they're running on a proprietary standard, they won't be good and widely used as they could be if they were brand agnostic.