How do bloggers get naked fan followings?

In my travels through blogland I've seen more than once that bloggers will have fans who send pictures of themselves naked or topless while they hold signs saying they are fans of the site. Example, starterupsteve. Granted, I'm not a man, but I'm just curious how the whole naked fan following gets started. Do I need to be in the porn business or something? If it helps, I love the show Family Business.