The other day I was in my advisor's office and he said "let me show you something you've probably never seen before: a fully legal version of Chinese Windows!".
I don't understand other cultures... Why pirate Windows when you can have Ubuntu for free?
It's probably more the quality of OpenOffice vs MS Office (and other desktop apps) rather than Ubuntu vs Windows per se.
A number of reasons: Everyone else is using windows, you're familiar with windows, all your software runs on windows, and installing Ubuntu requires a lot of downloading when a version of Windows is a cheap disk from a local store.