Sure, fans care about total viewers, and they are good numbers to throw around in press releases and in general because it's an easy number everyone understands. If you start getting into discussion of the 18-49 demographic with the masses of fans it begs a lot of questions, starting with "huh?" and usually ending with some comment like "That's crazy, people over 50 have more money to spend than some punk 22 year old kid!"
Nonetheless, we focus on adults 18-49 because for primetime, it and adults 18-34 are the best generic measures of a show's success. The ad rates are set based on the amount of younger viewers and success in selling advertising is typically the biggest factor in whether a show gets renewed or canceled.
As an example, earlier this week Bill Carter had an article in the New York Times about how although Dancing With the Stars has actually had a couple of wins over American Idol, it basically just amounts to chest thumping in press releases. American Idol charges $642,000 for a 30 second commercial spot while Dancing With the Stars is selling 30 seconds of ad time at $209,000 per spot.
Mr. Carter explains the huge difference in the advertising rates:
Why the huge disparity? Because the two shows, while now close in overall viewers, have vastly different audience profiles. These can be summed up in simple terms: “Dancing” is heavily female and older; “Idol” is heavily female and younger.
“Dancing” is a show with a serious tilt toward women viewers over 50 years old. Last week, for example, of those 23 million total viewers, 10 million, or about 43 percent, were women over 50. (Another 3.9 million were men over 50.)