Another example of a game using real names is iRacing, though real names are used throughout the game, instead of just on the forums. Again, the idea is to discourage anti-social behavior (intentional wrecking, profanity, etc), and this is part of their aggressive policing against griefers. In this case, such a prevention is especially necessary for a racing game of this type. I don't frequent the Blizzard forums, so I'm not sure if there are enough douchebags there to justify such measures.
It's true that iRacing uses real names (I play both iRacing and WoW), but one significant difference here is that you know that going in to iRacing - you never have had a pseudonym for it. For Starcraft 2, the same is true - the game isn't out yet, and you're being made aware that the official forums will not be anonymous. But World of Warcraft is a different story; if they do in fact apply these changes to the official forums, it's changing how they've worked for the past five years.
I think the reactions here are overblown, however. RealID is 100% opt-in in the game itself, where it replaces an avatar's name on your friends list with their real name. You have to accept an invitation from someone to exchange RealID information.
As for the forums, I think posting under your real name might just have the effect they're after - people being a little more thoughtful about the words they're using to discuss what happens in a game. It certainly works for iRacing.