I don't really think so. The people who seek out specific documentaries are probably doing so for a reason. Not a lot of people are willing to sit through a three part documentary like Zeitgeist unless they're at least vaguely interested in the topic. Popular documentaries that make the rounds largely have no 'teeth,' and that's why they become popular. Think of Michael Moore's documentaries, they're about hard hitting social issues, but they make you laugh, they make you feel good, and most importantly, they're filmed like many narrative films are. Documentaries that have 'teeth,' and actively work to change society are usually specialized, and people have to seek them out.
that's just my 2BTC. I've recently graduated with a minor in film (nothing special, I know), but I did take a course on documentary films.