A Messy Transition (Part 2): Windows XP, Vista, and the 2GB Barrier
 

Shortly after publishing A Messy Transition (Part 1) we received numerous requests for similar user address space usage testing under Windows XP, as we had previously done all of our testing on our standard Windows Vista setup. Although we were not expecting a great difference - certainly Vista will use more resources than XP because it's a newer and heavier operating system - we decided to follow these requests anyhow. However what we found completely blew our expectations. And with that said we'll immediately dive in to the results of our findings.

http://www.anandtech.com/showdoc.aspx?i=3044

Bottom line, I know you have a problem with the 2GB barrier but we have a bigger one: to sell more Vista.

that's not a problem, it's an advantage, if Vista keeps not selling and XP keeps on sticking around, Game makers will want to increase their target audience and demand DX10 for XP:)