Whilst it's obviously just a move from AMD's perspective to get the short term sales of their Radeon 5000 parts up by making DirectX 11 more important, it will at least eventually benefit everyone once they also get the hardware out. Moreover, DirectX 11 benefits people who even just have DirectX 10 graphics hardware, including those who bought from Nvidia, S3, Intel, whoever. Sure it's not a saintly move by ATi, they're doing it to benefit, but it's not got the long term effect of segregating the market because eventually all vendors will support DirectX 11.
That,s what basic marketing is about & if NV was first out with a DX11 card & was doing the same i would be happy as everyone would benefit as you say in the long run as the DX standard is for everyone & nether ATI or NV can restrict on who can have DX.