guys, we're missing the point. it's the inner beauty that they're rating.
Well, maybe not so much that...but they take into account the outer hotness and the "hotness" that is their celebrity status and attractiveness at the moment. Their reasoning was that she is a big-time party girl that gets wild and crazy all over the place, so in their view, that makes her "hotter." Note Paris Hilton being in the top 5 last year or two years ago, I forget. She was in the spotlight for her show, her sex tape, and her partying. In any event, she's not on the list this year (good riddance).
Not saying that I don't agree with some or many of the names on there...some of the girls they put on there are just ones they had in the magazine that they want to expose again. There's probably a few that guys have never heard of before that just made it because they were in Maxim last year.
Example of a bad pick - Cameron Diaz is way not hot to me. There's no way I would even have her on the list let alone at #20! Girls like Katherine Heigl though...they definitely belong on there.