This isn't just to make commenting more social (i.e. pushing friends comments to the top)-- I imagine it's also largely to hold more people accountable for their comments (w/ their reputation) so that there aren't as many nonsense/flame/bigoted comments like there always have been on Youtube, and in turn get higher quality comments (e.g. Quora vs. Yahoo answers analogy)
> hold more people accountable for their comments (w/ their reputation) This belief has been thoroughly debunked by Facebook comments. There's absolutely no reason to believe that Google+ will be any better, particularly since the ghost-town nature of G+ means people will rightly assume they can flame away and nobody they know will ever see it.
For example: typical bad Facebook comment = angry rant at Sean Parker from person who seems genuinely angry
vs
typical bad Youtube comment = some nonsense troll/needlessly racist comment.