Thats the same way the MPAA is.  Movie A has an artistic, well made sex scene showing minimal skin (front and back but no porn contact.  Movie B has knives, bombs, guns, and blood.  As well as a bunch of deaths.  Movie A is rated R and Movie B is rated PG-13.  That has never made sense to me.
It's truly insane what the American culture teaches its youth; sex is bad, but death is good.