Bethesda learned their lesson with OB and just like FO3 and New Vegas they are coming out of the gate with a mature rating and that's just smart.
Precisely -- and it has nothing to do with what content you
want to put in the game. Rather, knowing that you've got an M rating in the first place allows the writers to just write. With the specter of a T rating looming over their heads, there's a strong urge to play it safe, which usually results in a fairly bland story. Probably an E-rated one actually, and then they crowbar in some gratuitous six and violence after the fact. Easier to do it that way because, starting from zero, they know exactly how much to add; but it's just pasted on.
If the game's known in advance to be rated M, none of that crap is necessary. Write a real story, no holds barred,
and it doesn't even need boobs because your audience is expected to be mature enough to appreciate a sophisticated plot on its own merits. You know... like it was before games were rated in the first place. This is the same franchise that brought us Daggerfall, remember?
Edit: Apparently certain slang terms for human mammary glands are censored. Also, for the record, I'm quite aware that most people over the age of 14 can handle mature themes and sophisticated literature. It's just illegal to sell them to you.