In this Feb. 11, 2011 photo, a Facebook page is seen on a computer in Montpelier, Vt. Facebook on Thursday, Feb. 17, added civil unions and domestic partnerships to the list of relationships that its users can pick from to best describe their romantic status. (AP Photo/Toby Talbot)
Most of the reason is that having to sign in with a Facebook account establishes a real identity and hit-and-run snipes and insults are harder to do when one can't maintain anonymity. So, like TechCrunch said, its trolls have dwindled and its comments are decidedly gushing -- but they prefer that over the sheer "anonymous" nastiness that showed up on a daily basis.
In journalism, we know the importance of using someone's name and spend a lot of time correctly identifying that person in a story. A commenter saying something rude, crude or malicious is easy when it's done anonymously, but requiring a real name and account to comment and that element tends to disappear. Does that mean it's neutering our free speech? Not really, but it is creating more accountability in a world that judges people for what they say and who they are online.