That's somewhat a good thing, although if you add the percentage of people that have DX9/10/11 GPU's and Windows XP, you get 28,53% of Steam users.
I really preferred that the DX11 adoption rate was higher. Perhaps by the end of this year. When you look at what a game like Crysis can do with DX9, and consider that in DX10 you don't have tessellation nor the better lighting features that came with DX10.1, but neither Nvidia or many games studios supported, I'd just prefer they do the best DX9 version ever, which will satisfy most people, and concentrated on making the best DX11 yet. They could just jump DX10 by this time.
They haven't adopted DX10 with Left 4 Dead or Left 4 Dead 2, and from the system requirements of Portal 2, it seems they improved the DX9 engine they already have. So, now that DX11 is out for more than a year, and predicting the game will only come out in a few months, that will make it two years after DX11 came out. No sense in spending money in DX10, when the best DX9 can do pretty well, and DX11 is a definitely a noticeable and worthwhile investment.
When you look at it, most DX10 cards out there don't have the power to run DX10 properly anyway, so all those would just be disapointed. Those users are much better off with a highly optimized DX9 engine like Source already is.
Take a look at the survey and all those DX10 "spec" cards:
Geforce GTS150, 8600GT, GT 220, 230, Geforce 9600, 9600M, 9500, 9400, GT240, 8400, etc
Mobility Radeon 4570, Radeon HD4650, 4670, Radeon HD 2xxx series, 3xxxx series (except for the 3870x2)
And even the 8800GT/9800GT is not such a spectacular card running DX10 either. And the same goes to the Radeon HD4830
And even modern DX11 cards are only good DX9 cards. Take the HD5670, which is slightly slower than the 8800GT, and everything AMD has below that card, those are all good cards for DX9, not DX10 or 11.
The first card in AMD's lineup than can do proper DX11 is the radeon HD5770.
The first card in Nvidia's lineup to do proper DX11 is the GTS450 (preferably overclocked. Preferably a GTX460, either the SE model or the 768MB, preferrably the 1GB model.
These DX11 cards are not very expensive and I think those with slower DX10 GPU's would be better with DX9.
Of course, there are exceptions that can handle DX10 well, like the HD4870, 4890, 4850x2, 4870X2, the GTX 260, 275, 280, 285, 295 but I added those and only came up with 18,25% of the total DX10 GPU's. I don't think that warrants doing a DX10 rendering path anymore, especially because that number will only decrease as the months pass.Edited by tpi2007 - 2/22/11 at 5:22pm