I imagine that quite a lot of the people on XP cannot upgrade.
Quite a lot are probably using it because their hardware is just not supported on new versions of Windows. The Vista change in driver model basically meant a huge amount of old hardware became useless. Another bunch of them are using it because they don't want to pay for a new version of Windows, which is prohibitively expensive to buy "off the shelf". So they "cannot" afford to. And another fraction cannot upgrade because their computer is just too slow or doesn't have the RAM to run newer versions. And another fraction have older software that isn't compatible or is not supported on newer versions of Windows (the reason most corporate and business customers are probably stuck there).
So actually I think quite a lot of Windows users are "stuck" on older versions, and in many ways they are worse off than Android users because there is not thriving community of Windows ROM developers making free upgrades.
