"But Windows XP has the most market share out there!  (A whopping 44%)  Of all operating systems on the planet, it has the most"

I think that's only true if you include Asia, where there is massive use of pirated XP.

According to NetMarketshare.com
Nth. America:  XP: 26%  Win7: 48%
Sth. America:  XP: 34%  Win7: 54%
Europe:           XP: 32%  Win7: 46%
Australia:        XP: 23%   Win7: 47%
Africa:            XP: 39%   Win7: 51%
Asia:              XP: 57%   Win7: 34%

In all regions other than Asia, use of XP is falling steadily and Win7 rising at the inverse rate.