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The decision to encourage instead of mandating, for now at least, takes the teeth out of it. But maybe it will still make a small difference. I suppose if you switch to your real name and have an impulsive "jerk" moment, and aren't the type that makes a habit of trolling insecure teenage girls on YouTube, it might cause you to think twice. Keyword, "might."
Even it Google made it mandatory, just because someone knows your name doesn't make you all that much less anonymous to the majority of people on earth. The risk of a broken nose just doesn't increase enough because a post identifies the commenter by name to have a real deterrent effect. Think about those jerk kids who tormented the bus lady. They didn't try to hide who they were, they were proud of it and wanted to show the world. Same thing with a lot of trolls. A lot of them think they are being funny and clever (and as much as I hate to admit it, a few actually are), they aren't all likely to be embarrassed by using their real name. They might change their mind if they run afoul of some of the 4Chan crew, however!
Oh, and as a rule I don't troll or make particularly nasty comments, but I'm not switching to my actual name on YouTube. It would make for asymmetrical warfare if I did so and got into a snit with someone who was not using their name. They could potentially screw with me using from my Google+ profile, and I wouldn't be able to respond in kind, so there is no deterent effect.