The internet is full of amateurs and skanks posing nude. The allure of Playboy was that genuine 10's (and there ain't many of them) posed and were photographed by the best photographers in the business. The highest standards were maintained. Celebrities that would not go near Penthouse or any other skin mag would pose for cover shots for Playboy.
Haven't seen a Playboy in ages, but the cover of the Dolly Parton you posted, with the "Co-eds of the Pac 10" feature, reminded me of the days when it was big news around here when an LSU co-ed would appear in one of these college spreads.