My theory is that Nielson families, the ones who actually count as ratings, are stupid. You could have millions of people watching a show every week, but if not enough people with tracking systems hooked up their TVs are watching the show, it doesn't count. That's how brilliant stuff that a lot of people watch gets canceled and how low-brow tripe goes on season after season. Look at who they are catering too. Doesn't help when a show is too expensive (re: Farscape, FireFly) or too quirky (WonderFalls, Andy Richter Controls The Universe) or just too good (Undeclared, My So-Called Life) and people just don't get it.
And people wonder why there's never anything good on. There's a glut of crap out there all clamoring for our attention (well, our money, via ad revenue as far as TV is concerned), but the good stuff is always hard to find. Remember this the next time you have to re-run some stupid reality show because you have nothing else Fox. And remember this the next time you complain that no one's watching your movies or buying your CDs entertainment industry. 🙄