While nVidia did get sections of the DX10 spec changed, to blame the poor performance of the R600 on that is a bit misguided. The R600 was just a badly balanced design, with things such as huge amounts of the die being taken up by the ring bus and 512 bit memory interface, leaving no room for more shaders, TMUs etc.
That alongside poor AA execution, the dire 80nm manufacturing process and teething problems with the new architecture (not to mention the very recent takeover of ATi by AMD at the time), was really what made the R600 a bit of a flop.
Firstly, the card had AA hardware, which couldn't be used without dx10.1(the original spec) being used in games, so it had to shift AA from hardware, into software done in programmable shaders, to say DX10 wasn't responsible for that is to simply not know what you're talking about. To say it was unbalanced is again incorrect. it WOULDN'T have had more shaders without the ring bus in, it had the right amount of shaders and everything else it needed, its still a VERY good card, in dx10.1 it beats the 8800gtx quite easily , without it its still faster in a few games, behind in the majority of games but not by that much. Considering TSMC screwed them, had it launched at 65nm, with 10-15% higher clocks it WOULD have been faster than the 8800gtx in a lot more things, if DX10 was released in its original spec and every game from Vista's release onwards was released in dx10 "proper" the 2900XT would have beaten the 8800gtx in almost everything, whilst also being cheaper and running cooler.
Hardly a bad card, as said dx10 hachet job screwed the card pretty badly, added to TSMC screwing up 65nm(as they screwed the pooch on 55, and now 40nm and probably previous processes in the past just before I was reading news about it), its a fantastic design in everything except its size/price , the implementation with both manufacturing and Nvidia/MS/dx10 against it meant it would never be as good as it should have been, considering what it was designed for and how it had to fight in the end, the fact it was so close to the 8800gtx in so many games and beat it in any games is a testament to how good a design it was.
Nvidia's biggest problem over the next 2-3 years, is Intel, TWIMTBP is going to die a very very fast death, Intel simply crush Nvidia in terms of money to spend on similar campaigns, without programmers designing stuff for their cards from day one they will lost out a lot to AMD and Intel will have loads of dev's working to make its hardware work fantastically. IT will be interesting to see how the whole situation plays out, Intel are buying up programming firms and groups of people who are aimed at paralel programming so they are looking to have plenty of people for drivers and sending off to work with dev's for optimisation. It will be most interesting to see final reviews of the Larabee, less for performance(because its their first attempt and they'll improve competitiveness easily, thats assuming they aren't close at first) but more for design and seeing just how different it is. Its very possible they could have wanted to go for something massively different but in the end its far more similar to a ATi core than we've been led to believe.
