Although ATi is their competitor, AMD's customers base are large enough that nVidia won't abandon them. I don't have boards equipped with chipset from either of the companies, but if you asked me, nVidia chipsets are generally better that their ATi counterpart, by a good margin. So enthusiast, or even general consumer brilliant enough to know and aware about performance will look to Nvidia first, then ATI, and then VIA etc...just my RM0.02
Yes, but wouldn't ATI have an edge over Nvidia, cuz they are AMD now. and they will know how to optimize their chipsets cuz they are the ones manufactering the processors for it.
Not necessarily, intel isn't the best at their own anymore either.
However it's almost irrelevant for one major reason, AMD is going to be taking back the Lion's share of the mobile and desktop OEM and low end market, which is now nV's bread and butter, and while nV can continue to make enthusiast boards, how much money do you really think that's going to be?
Nowhere near what it is now (likely nV best time ever having gobbled up ATi's intel sales, and still being able to sell their AMD solutions as the main ones in the previous pipeline) while I don't expect things to change soon, likely by this fall (back to school and xmas buying time) you'll see the landscape change, especially with the OEMs.