For example, 30 Rock is by no means a ratings juggernaut. Just last season, out of all primetime network shows, 30 Rock ranked 86. However, it scored around a 3.0 in the 18-49 demographic. A 3.0 is pretty good, especially for a show on NBC. Because it's been able to maintain a decent viewing in the 18-49 demographic, NBC keeps renewing it.
To understand more about how ratings are figured out, click here.
Advertisers love younger viewers. Especially viewers in the college age range. We're the ones buying the newest gadget, seeing the latest blockbuster and wearing the new styles. This is why we have the power of choosing what airs on television.
The reason LOST (I know, I have an addiction) was given free reign to do whatever it wanted on the show, was because it had millions of the key demographics tuning in each week. To air an ad during the final episode of lost, advertisers paid $900,000 per a 30 second spot. I'm sure ABC is wishing they could somehow bring the show back for another trek through the jungle.
College students/young adults have the upper-hand when it comes to what stays on the air. The Good Wife had an average of over 13 million viewers for its first season, however it came close to getting cancelled because it didn't score very high in the key demos.
What I'm arguing is this. As a young viewer, we have a strong say in what stays on television. All we have to do is watch.