I was just trying to outline this conundrum to a less savvy colleauge the other day. I've been swimming in this pool for many a long year and, like many here, have a perspective, and a somewhat jaded view, that your average user doesn't.
What G serves up (disregarding the content and algo) hasn't really changed since it first came online. It's old-fashioned 'SERPS', like we used to go and get from Altavista, Hotbot, Lycos and those other has-beens.
Facebook serves up something completely different, and to the average web user it is much more engaging. In a way it's a bit like the old concept of free e-mail, but mostly without the spam, which makes it less bad for the users. With some ajax thrown in it's pushed rather than pulled, and smart threading makes it feel interactive too. There's no rocket science here - they're just doing stuff to keep the users content and so far it's working out ok. (Disregard the share price, that's a side show).
We webmasters tend to be highly aware of the politics and machanisms of the web, but the to the average user such concerns are irrelevant - most of them just want to communicate. They think pandas and penguins can be seen in zoos, Florida is in America, etc. Perhaps that's unfortunate, but it's how it is.
Meanwhile a 'Battle of the Titans' is taking place behind the scenes. The dumb users (who are totally unaware of this) are gradually upgrading their smartphones and acquiring tablets when their ageing laptops croak, and mobile sims are giving them access to the internet anywhere rather than just at home, so the battlefield is mobile.
Unfortunately for Google, their thing called 'Plus' is something that nearly all of these dumb users haven't heard of (I've asked around of the 'unsavvy' and this is my unscientific finding). Almost all of them have a facebook login, added their friends a while back, and aren't actively seeking an alternative right now. Why should they?
Where is this going from here... who knows? I'm really not surprised that G has taken the gloves off. It's time to get serious. Trying to strong-arm the dumb users into using G+ won't work unless it's done in a really smart way, and that's a big challenge. The real issue for FB is how to integrate a compelling web search tool and get their users using and liking it - not just in the 'click a button and "Like!"' sense, but in the 'really appreciate and find it usable ongoing' sense. Bing is not that. They would be better off developing their own (or buying something in) if doing so is to be a realistic possibility. The web desparately needs a viable alternative or it's going to end up like Walmart, minus the competition.