By comparison, OS X 10.1 was the latest version of OS X available at XP RTM. OS X 10.2 would've set you back $129, 10.4 another $129, 10.6 another $30, and 10.7 another $30. (I don't believe that you can skip OS X release-level updates, but I'm not a Mac user, so I don't know; if you can, feel free to correct me.) Even if you magically bought a computer in 2001 which would still run Lion today, you would've spent $310 on OS upgrades, for a period of time for which upgrading Windows cost less than half as much.