I get your point, but I think that's simple too: you received the post because it was sent to you. Or in Google's vocabulary: because you were in the circle it was shared with. I can agree though, that this slightly more confusing than the Facebook model: because your friend posted it.

I really like the idea of suggesting Google+ "celebrities" to follow; you should suggest it with the feedback tool. I recommend Tom. :)

  http://profiles.google.com/myspacetom