Those Steam stats provide some interesting insight, and actually show that nVidia is gaining share vs AMD in the DirectX 11 stakes.
The AMD 5770 holds the single largest share at 13.23%, but this share has been in decline since September, and currently holds an 18.63% smaller share now than in September.
GTX460 is the second largest single share at 10% dead, also declined since September, and currenly 15.11% smaller now than then.
Conversly, however, the GTX560's share (third largest at 9.47%) has grown by 66.43% in the same period. This gain in share is only exceeded by the GTX550, GT440 and AMD 6670, however these three cards hold a very small total share (accounting for just over 3% combined) so the gains in real numbers are small.
Out of the top ten largest gainers 6 are nVidia cards compared to 3 AMD and 1 other (which could be 7970 I suppose).
Out of the top ten largest losers 8 are AMD cards compared to only 2 nVidia cards.
The top ten largest shares are split 50/50 with nVidia and AMD holding 5 spots each, however three of the nVidia cards are gaining share (GTX560 66.43%, GTX580 29.47%, GTX570 15.85%), compared to only two AMD cards, one of which is only a minor gain (6950 24.39%, 6870 1.18%).
Of the total DX11 market, AMD hold a 55.45% share vs nVidia's 41.86% share, however nVidia's share has grown from 36.93% in the Sep-Jan period (a 13.3% gain), where AMD's share has contracted from 60.79% (a shrink of 8.8%) in the same period.
I'm not sure it's either Intel on-board or VIA/S3. They both show up as identified chipsets in the other Steam results, plus are they even DX11?