From my experience and little of my friends', ATI drivers sucked heavily compared to nVidia (for one, they didn't work for me on Windows 2003 with 4GB of RAM before Cat 9.4 - don't even know if that one does, I removed 2GB of RAM to use the ATI card).

With that in mind, and being a driver writter myself, I can see why NV would do this. I have too often had other company's drivers make the problem, and I always had to make workarounds to make mine work with theirs (no I couldn't just prove it was their fault - I ahd to make workarounds earlier).
Nowadays, I provide sufficient evidence to convince my customers they need to swtich the other company's product or a lot of other software similar to mine will not work with it (that Joe Average dumbass can install). It works!

I'm sure they think it's wise in market terms as well - but when it comes to driver interaction - don't uinderestimate the stupidity other people can make! Especially under pressure - that your driver (company) will end up being blamed for.