why new moon is rated PG13!!!

Apparently the reason that the new movie New Moon is rated PG13 is because of the amount of men going around  topless(Jacob and co, Edward) and the fact that there is one scene in the movie where the Volturi are totally naked!!! Actor Jame Campbell-Bower revealed in a interview with MTV that in a flashback that Carlisle has in the movie of when he first met the Volturi,  he actually met them while they where having a bath in an Ancient Roman bathhouse!!! Apparentely Jame Campbell-Bower said that it was grand filming it, but when Carlisle entered the scene full clothed, it got kinda awkward!!!