If Apple's success has taught us anything, it's that "UI polish" trumps pretty much everything else when it comes to making money from software, and it is hard to get right (or else everyone's UIs would be just as polished as Apple's).
So if Facebook is behind Google in "Just UI polish" they may have very much to fear, indeed.
Apple isn't afraid to have a bad idea and then toss it out because, after all, ideas are cheap. If you build a turd and you polish it, are you still going to release that polished turd? The Apple way is to design it the right way from the start, THEN you polish it.
It is true that Facebook may just copy the best innovations of Google+, but that puts them in a defensive position and obviously isn't what they want. We've seen what happens to giants who bank on leveraging their entrenchment in the current market.