Staisitics such as those can be misleading. The biggest flaw is, of course, how long XP has actually been on the sales shelves. Also, how many XP users have converted to Vista/7 etc. A better indication of the future of Windows 7 might be in a consumer report such as this
"
"Windows 7 software unit sales in the U.S. were 234 percent higher than Vista’s first few days of sales," NPD
reported earlier this month. "Revenue growth wasn’t as strong though. A combination of early discounts on pre-sales and a lack of promotional activity for the Ultimate version resulted in dollar sales that were 82 percent higher than Vista."
But comparisons to Vista aren't a great indicator of Window 7's overall success. Vista sold 59 percent fewer copies than Windows XP, when comparing each OS's first week, according to NPD.
So, it seems the big story here is that Windows 7 outsold XP by two times, over the same period.."