In a recent poll of active users on WinCustomize, 87% of the respondants were men. Which leads the to question, did they find out about WinCustomize by typing "skins" into a search engine?
The result doesn't surprise me. I can only comment for my wife, but she honestly doesn't give a stuff what her display looks like - her PC's just a tool, a means to an end. I think men get a lot more territorial about their desktops - the 21st century equivalent of leaving scent marks around your domain ...
Perhaps it has more to do with how much artistic sensibility one has. Perhaps men have more of this than they usually allow the outside world to see and this is a means of expressing it without the worry of social judgement of their "manhood". *Some* (some, not all) guys are stupid like that.