CS5 runs fine on ATI cards. In fact, the only application that really takes advantage of a CUDA card right out of the box is Premiere's Mercury Engine. And on the Mac, only two CUDA cards are actually supported (the GTX 285 and the Quadro FX 4800). So chances are, even if the new Mac Pros DID ship with NVIDIA graphics options, the card wouldn't be an Adobe-supported one right off that bat.
Also keep in mind that the Mercury Engine even makes improvements in performance over Premiere CS4 running in "software" mode because of its superior CPU scaling and memory handling.
As for the rest of the CS5 apps (Photoshop, After Effects, etc.), they rely on OpenGL, not CUDA. The exceptions would be some aftermarket Ps/AE plugins engineered for CUDA acceleration.
The biggest so-called conspiracy with the whole CUDA thing with CS5 has been Adobe's limited support of CUDA cards. While there are dozens of CUDA-enabled graphics cards, only 5 are supported in Windows and 2 in Mac OS. The rest of them are turned off because "they haven't been tested." Adobe is starting to get a lot like Avid in this regard.
Hopefully, when Adobe enables support for Fermi-based CUDA cards as rumored, the new Quadro 4000 will be supported. That's a killer professional CUDA card for under $1,000.