Short version: Someone at Blizzard played Farmville or Mafia Aquarium or whatever on Facebook and said, "We need World of Warcraft to spam the hell out of Facebook; it'll attract new players and legitimize us in the face of mainstream culture!"
World of Warcraft Strategies: The Point of RealID and How to Stop It.
By bringing the big three Blizzard franchises of Warcraft, Starcraft, and Diablo under BNet 2.0, Activizzard has created, without a doubt, the critical mass of players needed to generate the initial wave of buzz. All that is left is to ensure the visibility of this massive following.
Now THIS is where RealID comes into play. Activizzard is planning to make it virtually impossible for you to hide the fact that you're playing on BNet 2.0. By publically outing its entire player base, the goal is to blur the us versus them boundary on Blizzard games. Imagine as people who wistfully shook their heads at video games suddenly find their relatives, friends, trusted employees, colleagues, and bosses to all be playing on this newfangled "BNet2" thing. With sustained releases of Starcraft 2 followed by WoW: Cataclysm, then SC2 Part 2, then probably Diablo 3 and so on, Activizzard can keep BNet tag alive and kicking on social networks for years to come. As the appearance that "everybody's on BNet" spreads, monkey-see-monkey-do will kick in without fail.
There was a submission a while back about some Facebook user defending Farmville as "not a video game" so "it's okay to play." While this may seem like hypocritical nonsense to anyone who's not a blithering idiot, it is also the type of blind cultural acceptance Activizzard hopes to engender for BNet 2.0.
I must admit that I didn't check into whether or not that particular post was true or made up, but from my experiences on social networks, I find the story quite believable. In fact, I would say it is incredibly common to find arguments and individuals of this caliber on Facebook. Unfortunately for us, these are also the people that BNet 2.0 aims to bring into the fold.
I know some of you will feel this sounds like a conspiracy theory. All I can say to that is that brilliant pieces of mass marketing often do sound like that.