If you think that then why the hell do you up OSX when it just going to be out dated 12-18months later with another upgrade cost.
Because with OS X, to buy the new full version, its $129. To buy the full new version of Windows, it costs well over $400, possibly $500 if I recall correctly. In two years, thats a big jump. Sure, most people don't need Ultimate, but I don't think that even Vista's lowest-end choice(which has few new features over XP) is less than $129. Basically, its much less of a hit on the pocketbook to upgrade OS X every two years than to upgrade Windows every two years.