People who use Firefox and Chrome care about having a good browser. People who use IE are content to use what came default with their computer and might not even care about running automatic updates.
What? I'm serious--you can't compare Firefox and Chrome users to IE users on how many of them keep their browsers up to date, because FF and Chrome users by definition are people who take an active role in downloading and installing web browsers. It's a selection bias, not a slam against IE or IE users.
