I understand what the expression means, and that's what I meant (though perhaps I could have been more clear). *nix (and libc) are exceptional in that they got first dibs on the symbols they wanted due to being there first. So it proves (while justifying) the rule that you have to prefix all of your symbols unless you're Thompson or Ritchie in the 70s. Even now, in newer C features, extra acrobatics are done to avoid name collisions (_Bool in C99 for example).
But this is really a side issue to my original point: C++ and PHP are categorically different since there aren't strong alternatives to C++ for many types of problems. Though it is possible that other languages are eating at the edges of what C++ is good at.
The actual origin of the saying is quite different:
http://en.wikipedia.org/wiki/Exception_that_proves_the_rule