That statistic only tells that most people prefer using Windows.
Actually that statistics tells you that most people couldn't care less which OS they use, and just used the one that happened to be on it when they got it. Since a good 35% of those 90% are still using IE6, it further tells us that most people don't even care enough to keep their useless OS up to date. What if the "average user" wants to use wireless Internet access, and linux isn't recognizing the wireless card?
The same thing that happens if the "average user" wants to use wireless Internet access, and Windows isn't recognizing the wireless card. What if the "average user" wants to install a piece of software that isn't listed in the main installer app?
See above.