You know that any games that are released in the next year or so have been in development for as much as two years already. So to think that DX11 games are coming out any time soon is wishful thinking. If it gets tacked on at the end of the development cycle, it's not going to be a show stopper and likely with look nearly the same in DX9 and DX10. In most cases, if you look carefully at the titles released from now to a year from now, you'd be surprised to find that development is still centered around DX9. Look at
STEAM's stats, most people are still using DX9 capable cards and those using DX10 capable cards on XP still outnumber those using DX10 cards in Vista (though admittedly it's close). Game developers and publishers are going to want their games to run on the lion's share of the hardware out there. Sadly that is still DX9, whether on XP, Vista or Windows 7. If you look at Windows versions, over 50% of STEAM users are still using XP. I like the bleeding edge of technology as much as the next geek, but I live in this world and the market rules what technology is used in this world. The market says that making games for DX9 is going to make more money than gambling on hardware and OS uptake in the following year.
Now games beginning their development cycles now will likely focus primarily on DX10. This is good for those using DX11 hardware because DX11 isn't a huge leap from DX10. So it will be easier to support DX11 features from a DX10 code base than it was to support DX10 from a DX9 code base.
To use consoles to base an argument that DX11 is going to be pushed into the forefront in the very near future is baseless. This generations consoles are essentially DX9. When the next generation comes out they may use DX11 hardware, but we are still a few years off of the next generation console. In the mean time game development is going to be centered around DX10, so the likelihood is that the API's for the next generation consoles will be primarily DX10 when they first come out.
Now to whether or not nVidia releasing DX11 hardware later than ATI is going to hurt them, sure it is. From a practical point no, but from a perception point, yes. Anyone buying a graphics card immediately after ATI releases the 58XX cards would be think twice about buying a DX10 card. Whether this is practical or not doesn't matter. The DX11 features may never get used during the cards useful lifetime, but having those features makes the purchaser feel more future proof. This is the same thing that happened to ATI when nVidia released the 8800 series. It didn't matter that nVidia didn't have DX10 drivers out, the hardware supported DX10 and that perception drove it's sales. It didn't hurt that they also performed really well in DX9 either. Coming late to the DX10 party really hurt ATI's market share, not to mention the 2900XT's lackluster performance. Of course having DX10 hardware for so long without a functioning DX10 driver hurt nVidia in the long run too (class action suit). Hopefully nVidia won't make the blunder that ATI did with the 2900XT. I personally don't think that nVidia is going to release their DX11 hardware as late as ATI did with the 2900XT. This could help the nVidia faithful keep their resolve in holding off to see what nVidia has to offer. In the end, I think it will hurt nVidia's market share somewhat, how much depends on nVidia's execution. If they can release a DX11 part no more than a few months after the 5800, and if it can compete performance wise, the damage may not be too bad for them.
I think DX11 is a fairly big deal, but I don't think it's as big a deal as some zealot's make it out to be. To listen to them, when they get their 5800 and power it up, they expect nothing less than God staring back at them through their monitors. I think it will take a few years before most of us will really appreciate DX11 and by that time everyone will have forgotten about the first generation of DX11 cards (other than who was first to market with one).