Devs like open standards? You listed a couple Bullet games. I have around 15 PhysX games. I guess devs prefer physX, and likely will even more with the version 3 toolkit.
Physx 3 could bring a change but not much, bullet is still more efficient.
There are like 4-5 HW physx games worth mentioning, rest is just physx milking.. And even these 4-5 newer games (Alice2, Mafia2, BatmanAA, AC and maybe Cryostasis) are all bugged/inefficient.. Same story with a dedicated gpu.
For example Alice2 with 60fps cap, physx - high;
near fluids and smoke it drops to 35fps >> that's with gpu usage at max 52% (570gtx).. yes great efficiency, same sheit in batman AC.
Btw speaking of open std., Nvidia is thinking of importing Physx to openCL. Im kinda surprised you never heard of it since you're such a nvidia "expert".