Who really cares whether this, for example: (http://www.youtube.com/watch?v=ry0dHtwD4TU) is metal or not? Mostly people who care more about being "fucking metal" than music. Is it such a surprise that liking a kind of music can be about more than just social capital?
Yes, as genres get more complex, genre labels also become more complex. And sometimes the defining characteristics aren't clear. So what? This isn't a bad thing. If all "prog" was the same, then it'd be boring. There'd be no point in having yet another prog band. You'd be constrained by the label into doing a certain thing. People rightly chose not to do that. A genre gets you 80% there in terms of guessing what a band sounds like, and that's okay.