Windows XP users, which amount to more than 50 percent of the operating system market, will be left out because Microsoft plans to "continue to focus on how we do a great job with Windows 7," according to Microsoft exec Ryan Gavin, who made the statement to The Register.
As the cards fall, Internet Explorer 9 is not downloadable for XP users and is only downloadable for those running Vista or Windows 7 because the browser uses DirectX 10 for hardware acceleration, which isn't available for XP machines.
DirectX 10, Gavin said, is necessary for HTML5 features.