The author seems to be missing a gigantic point of order here. The reason why Facebook is algorithmically able to determine groups for you is because you, the user, have already entered in fields for Work, School, Location, etc. So the user has had to do a small amount of shit work for Facebook to do its magic. Of course, that's a very small amount of work relative to manually placing friends into circles. But G+ doe…
I think that the part where entering your info into Facebook appears less like shit work is that it's typically factual and structured: I worked there, I studied here, these people are family members. Google +'s circles are completely up-to-you, for better or for worse, and you hit ambiguous parts more quickly: is that guy a friend or an acquaintance? Should I put him in "Tech", "Ruby", both? But of course, as you go…
a) Creating a Facebook-like profile system, with more regimented fields and discrete data.
b) Totally disregarding users' privacy by doing it for them.
All of these are technically possible for Google, but they also have their major drawbacks. Where Google has been able to do it without downside - your private list of closest GMail and GChat contacts - it has.