I think that's illegal in many European countries to match the ads so closely, so it is unlikely that Google's had this in mind[1].

In my opinion, the actual reason is slightly gentler. There is a lot of research that says that people behave more responsibly under their real names.

(I'm short on time right now, but please let me know if you're unable to find the papers within five minutes.)

[1]. There is a huge difference in the privacy laws between the US and the EU. Shortly, in the EU you own your data, not the company hosting it.