Female vs. Male Nudity Onscreen: Why So Lopsided?

Yesterday's post on Anne Hathaway's nude scenes in Love and Other Drugs got a lot of you talking about the imbalance of male/female nudity on film: More specifically, why aren't there more penises on the big screen and cable? (Except for the errant Lucky Luciano penis, it's all boobs all the time on Boardwalk Empire.) Said MANGOPHD, "As someone who grew her own breasts, I must say, I'm tired of breasts on TV ... penis time folks." Our own David Edelstein chimed in to point out that "It's not beside the point that you can't have schlongs in an R movie. It's the whole, uh, ballgame in that respect." With the johnson off limits, is there any way to even the playing field? Or is the issue totally overblown? (Needless to say, no pun intended.)