Fitz and natureboy both raise good points.
And I'm gonna have to go ahead a disagree with the College Humor video. You can't compare a boob to a dick. A guy showing his cock and balls on screen would be akin to woman show her labia. Now, how many times has there been exposed female genitalia on TV? On HBO? Admittedly fairly often. But for every explicit pussy shown on HBO there are at least a comparable number of cocks as well. Now I can't speak to
Boardwalk Empire or
Girls, as I've never seen those shows, but I have seen
True Blood and
Game of Thrones. Now for
True Blood I've only seen a handful of episodes, but in those episodes I haven't seen a single guy go full frontal, nor have I seen single girl go full frontal either. There are a tonne of boobies in
True Bloood, that's true, but the tit shots are always fairly brief, often no more than a few seconds. Whereas there is a literal fuck tonne of shirtless guys in
True Blood, and it's not unusual for a guy to go the better part of an episode with his shirt off.
Now for
Game of Thrones, which I have seen every episode of, (and read every
A Song of Ice and Fire book thus far) so I am more qualified to speak on it. There is a lot of nudity in it, but most of the nude scenes are done by the whore characters, simply to "sex it up" a bit, and like real life whores, they aren't real people and so they don't count. As Dan pointed out there were three instances of full frontal male nudity in the first season. But other than the whore Ros flashing her hairy cunt to Theon, for less than a second, while she was riding the turnip cart to White Harbour on her way to Kings Landing, I can't think of a single example of lower frontal female nudity in season one. In fact I'm willing to bet that the scene in season 3 when Tyrion and Bronn took Pod to the whore house, had more muff shots in it than in all the other 30 epsiodes combined. But yeah, there are a lot of jugs in Game of Thrones, but there are way, way more shirtless guys than girls.
Now a big reason why dick shots are so rare on TV is because nude scenes are usually sex scenes, or post cotial scenes, and as such the guys dick would be more or less erect. And the only thing worse than a big floppy hammer on TV, would be a big throbbing, veiny, pre-cum dripping monster, wagging around.
And as much as some women might claim they want to see more dongs on TV, often when they do see one, their reaction is "EEK A Penis!" like in that
South Park episode.
http://www.youtube.com/watch?v=Mem-0JgHsCUBad quality clip I know, it was the best I could find on youtube.