My point is they could be slower at that price point, nvidia will still sell cards with dx10 now and until they got their dx11 cards out, their sales will not go down to zero until they have any dx11 cards until new year.
People are still getting 260/275/285/295 over ati's dx10.1/11cards and until there are a few games out that show a big difference some people will still buy dx10 cards if the price is right.
Firstly, Nvidia worldwide barely have any stock of the 285GTX, its all but dried up lately, 275's aren't much better, only the 260's have major stock around which frankly the 4890 is easily faster than, the 4890 outpaces the 285gtx in almost any dx10.1 capable game which, with dx11 games starting to come out already, and several dx10.1 games out, means it will largely be faster for some time.
But as said, the next gen midrange, has rarely beaten the high end previous gen, theres no need to. Nvidia, nor ATi have ever planned to significantly beat the previous high end with the new midrange, the only idea is to produce the same core smaller and noticeably cheaper, only hampered right now by low yields, as yields improve price comes down, the 4890/4870's are at max yields they'll get to, they won't get cheaper now(except when replaced to get rid of existing costs).