We all know how Google chose G+ first adopters; we are from geekosphere.
Google let the geekosphere crowd to form/build themselves from scratch via Circles concept and at the same time warm themselves up to the idea (of liking and using social networking). Google wants to make a different social network.
Quite likely Google may be using geekosphere ideas as they make re-factoring decisions about G+ on a daily basis. Perhaps without knowingly we became virtual (and unpaid) employees in Google's ideation process.
Google does not want to open G+ up prematurely as that would instantly cause idiotsia(*) to pour in, eventually causing geeks turning their back and idea factories would have been killed off instantly as a result.
If they want to make a difference they need to be different and this time the difference will come from wisdom of nerds rather than banal "wisdom" of crowds. This makes sense and it is in line with their geek-oriented culture. It works out well for me.
(*)Idiotsia: People who are not Intelligentsia.