I disagree, and believe that if there were more 5XXX volume, nVidia may of lost some discrete market share. DirectX 11 and tessellation are important and one can see that it is important for nvidia as well, moving forward.
Speculatively based solely on the units shipped and AMD's revenue figures, I am not sure it would have made that much difference if there had been more shipping HD5xxx units.
Sure it might have been slightly beneficial and prevented some desktop share erosion, but based on the increase in AMD revenue vs increase in units shipped, and the fact that NV increased discrete marketshare, it seems reasonable to assume that NV gained a lot in the low end (where there are no HD5xxx cards), so HD5xxx shipments would not be hugely relevant.
That being said, the upcoming launch of low end DX11 products for AMD might help them in the low end to get back some marketshare, since they will have a technically superior product in terms of API support and (probably) a lower power and cheap to make product which will be welcomed by OEMs.
At the moment AMD has no real advantage over NV in the low end high volume market, which makes a strengthening NV position there quite possible/probable, and would account for increased overall desktop discrete share.
Of course, nothing can be confirmed without either NVs figures for revenue growth, or just simply a better breakdown of numbers (anyone want to pay the $1000 for the full report?).