I should start out by saying that this is far from my only reason for going to Vista. Lets not get into any kind of debate here on Vista, I'll just say that in my opinion it is inferior software.
I do understand where you are coming from, but I don't think its as simple as you think. At the bare minimum, both parties are at fault. The bad part is, neither will do anything to fix it.
The problem is not because ATI won't write drivers for the cards, as those are out. Plus, most other ATI tuners work OK in Vista. The problem lies in the way the MMC interfaces with the OS. The MMC interacts with Windows XP on the service level. That is no longer allowed in Vista. I think this problem is compounded by the fact that the AIW Tuner is accessed directly through the graphics interface. I believe thats why they can't just modify the existing TV Tuner softwareto work with AIW in Vista. At least thats my understanding. Its also my understanding that there are workarounds out there.
I think it sucks that we won't see Vista support for AIWs, but its not surprising. Its no trivial think to re-write the software from the ground up to work in Vista. Further, MS (and probably ATI), knew this would happen as a result of their new kernel, and weren't overly concerned with it. I think this is because ATI had already leaked that the x1900 series AIW would be the last one in the line, and that they would be discontinuing support at some point.
It sucks, but thats the way it is. And keep in mind, this is coming from someone that has owned several generations of AIW card, going back to the 7500 days.