Valve Software believes that the jump to DirectX 10 is not yet worth it, and has the data to back up the claim. According to statistics from Valve's Steam software distribution system, there are about 8% of gamers who use Microsoft Windows Vista compared to 90% who have Windows XP. Meanwhile, over 11% of computers with Steam installed are equipped with a DirectX 10-compatible graphics processing unit, though only about 2.31% of users have a combination of a DirectX 10 GPU and Windows Vista. "There are far more customers with DX10 hardware running on Windows XP than Windows Vista. If you're going to try to take advantage of that hardware, your customers are telling you, make sure it works on DX9 API. Right now with the flexibility of DX9, we can take advantage of DX10 hardware functionality through DX9," said Gabe Newell, the founder and managing director of Valve Software.
News source: Xbit Laboratories