[Xlythe]

It has more to do with the atmosphere than ad targeting. Pseudo names, screen names, random characters that can't always be pronounced scare away people who don't spend much time online. In most social settings, it's common for people to share names, for it to be pronounceable, and for it to be familiar. Like the "Trash" icon being where you dump your unwanted files, or the "Magnifying Glass" being where you search, you want users to feel familiar with your product. Google+ is pruning away a bit of the geek subculture so it doesn't become a huge majority and scare away a much larger crowd.

If Google+ ever becomes a household name, there'll be much less emphasis on real names. The risk of a super majority on Google+ by a minority in the real world will be gone.