I think there are two main parts to Facebook's seeming ability to "get away" with all sorts of things. The real name policy is one but simply having shitty privacy/sharing controls (compared in this case to G+ and its Circles which make it easy to pick which groups you want to share a post with).
Facebook has a huge userbase. "Critical mass" is definitely valuable but as other social sites have shown, it's not enough to make you invincible to competition. I think that the issue with Facebook is that not only is "everyone" on it, but it was the first such site to really get everyone on it. MySpace was huge with the under-30 crowd and yeah, even some people's moms got accounts but Facebook was really the one that got all of your non-techie relatives, your boss, your doctor, your local bar, and your neighbors to all sign up.
While I would have no issue just pulling up stakes for G+ (real names or not) because I like the interface, the mobile app, and the granularity and easy accessibility of sharing settings better, I have loads of friends and acquaintances who don't care about the real name policy and still claimed to hate G+. The most common reason they gave was that it was "too hard" or "not like Facebook".
Unless those people see enough reason to overcome the friction of learning a moderately different service, they'll never leave the comfort of Facebook. Hell, even minor changes to Facebook are inevitably followed by weeks of complaining (on Facebook, natch).
Which brings up the second point: when none of these services are compatible or built on any common protocol (like email), you can't just pick the "provider" you prefer with the interface you like best or the most appealing TOS. I have a Facebook account and like a lot of other people, I set up a G+ profile when it became available.
The issue is that it can only go one of two ways: everyone leaves Facebook for G+ (or any other competitor) or I need to maintain two separate profiles and post things I want to share on two separate sites, defeating the entire purpose of the services to allow casual sharing with large groups of friends and acquaintances. Actually, there's a third way it can go and it's the way that ended up happening: hardly anyone uses G+ outside of some niche areas and in herd mentality terms, that means it's a joke and only deserving of derision.
I'm sure something will come along and replace Facebook eventually but I can't imagine it will happen by literally trying to build a better Facebook. It'll happen when people start using different types of services for that sort of interaction and Facebook sort of just trails off as that annoying place where the only ones left posting are radio stations, meme pages, and your aunt that likes to post pictures of those "minion" guys.