imho, MS manages to sell millions of copies of windows because of its user interface; say what you want about windows randomly crashing, the crappy security, etc. -- but it's UI is the one most people are most comfortable and familiar with.
the X/windows UI on most linux distros, while vastly improved from the dark, early ages of linux, still doesn't quite match windows'.
what's more, a lot of people got hooked on MS office early on. 1-2 combo ng MS yan