I hear and see the fans of less popular shows often rail against hits like American Idol and the CSI franchise. I understand the fan's lament, though I do not personally share it. Although I watch neither CSI or American Idol, I don't fault the networks for airing them. The business is pretty simple - there are multiple ways to come at it, including the age and gender demographics, but more viewers generally means more money.
While there may be no extra premiums paid for massive scale, since advertising is a business that pays based on scale, the bigger your audience, the better the business. Size certainly does matter when it comes to television. If not overall size, than size among demographics that are important to advertisers.
I do watch some shows that are considered more mainstream and enjoy them. I love FOX's House and though it has fewer viewers than House, I love ABC's LOST as well. Outside of sports, all of my other viewing could hardly be considered mainstream when compared to the ratings a show like Idol gets. Certainly my favorite show ever, HBO's The Wire couldn't be considered mainstream compared to Idol. It didn't even draw 2 million viewers typically.
It seems though the concept of mainstream is different to everyone. A show with even 2 million viewers for example, might be considered mainstream versus a show that only reaches 800,000.
If anything, what's surprising to me is that from the outside looking in, it appears as if the major networks do not attempt to maximize the opportunity in front of them. They each have a few cash cows each (except perhaps for the CW) that seemingly then subsidize the lesser performing shows ratings-wise.
The thing to keep in mind is that save for a very few special events like the Super Bowl, no program gets the lion's share of the viewing audience. American Idol is a big hit, but you know what? When it was on last night from 8pm-9pm, 78% of the televisions turned on were watching something else. 22% were on Idol, and that's indeed very, very impressive in this day and age. But don't lose sight of the notion is that overwhelmingly, more people watching TV were watching something else besides American Idol. Seventy-eight percent of people watching TV last night at 8pm.
I'll probably be revisiting this notion regularly.