In the beginning Facebook was far more restrictive in requiring a university email as well as a real name to sign up. If it had instead launched based on an open invitation system and not policed pseudonymous accounts then marketers and trolls would have ensured it remained an insignificant niche site.
If anything, real names were far more critical to Facebook's success than they might be to Google+
Also, Facebook doesn't use your name to find your friends, they use your friends list to suggest their friends might be yours as well.
Reason and method are both different.