well, ATI isn't delivering anything at all on a gpu these days, just ask wreckage.
Nvidia made a calculated gamble when they bought ageia. They have spent a lot of time and effort investing in physx, and especially over the past 12-18 months they've used it as a selling point for their cards. There's nothing illegal/immoral/etc about that, but I do think that it would be more astute for them to implement it differently.
As an example, if you could run physix with an amd gpu as the main gpu and nvidia as the physx gpu, that could go a long way to bringing physx to a greater audience. Devs would be more comfortable making physx a larger part of their game if they felt confident that most users could take advantage of it, and there are a LOT more 2-4 yr old nvidia mid/high gpus out there than there are amd cards.