Gabe Newell, president of Valve Software, believes that Microsoft made a serious mistake releasing DirectX 10 for Vista only, excluding Windows XP. I have to agree with Newell.
According to an online survey by Valve Software, only one in fifty players who access download service Steam has a DirectX 10-compatible graphics card and Windows Vista installed. In an interview with heise online, Gabe Newell, president of Valve Software, said that Microsoft made a terrible mistake releasing DirectX 10 for Vista only and excluding Windows XP. He said this decision affected the whole industry as so far only a very small percentage of players can use DirectX 10.
I'm not going to get started on the debate as to whether it was possible for Microsoft to back-port DirectX 10 for XP or whether the decision to make it Vista-only was a crass sales technique. That's another argument altogether. But it's hard to escape the feeling that DirectX 10 is both unnecessary for gamers and being shunned by the games industry.
The first weak link in the DirectX 10 chain is, without a doubt, poor gaming performance under Vista. I won't go as far as to say that gaming under Vista sucks whole lemons (it used to), but it's nowhere near as good as under XP. I'm not a heavy gamer but I still notice the performance drop on Vista compared to XP. This is why over 90% of gamers taking part in Valve's survey still use XP (compared to a shade under 8% using Vista). Hardcore gamers are smart and are usually unwilling to mess with their systems unless that results in better performances.
Then there are the hardware requirements. Only 2.3% of users surveyed were using Vista along with a DirectX 10 compatible GPU (the NVIDIA GeForce 8800 being the most popular). Graphics cards offering DirectX 10 support won't break the bank any more (you can pick up an NVIDIA 8400GS for under $50), but systems not specifically designed for gaming are unlikely to come equipped with a DirectX 10 compatible card.
Then there are the games. DirectX 10 compatible games are thin on the ground. This will change over time but that still leaves the fact that DirectX 10 offers little extra for gamers. From the Heise article [emphasis added]:
The Half-Life 2 Orange Box, which will be released for PC and Xbox 360 on 12. October, uses DirectX 10 functionality only for accelerating some mimics. Visually, however, it was virtually impossible to differentiate between the versions.
If Microsoft had managed to release DirectX 10 for XP, this would have acted as a springboard for gamers into Vista and given game studios the ability to show the DirectX 10 advantage to a wider audience. As it stands, with only 2.3% of gamers able to take advantage to DirectX 10, it's not worth making the effort.
My guess is that DirectX 10 won't hit mainstream until Microsoft have stopped talking about Vista and moved onto Windows 7.