I'm pretty sure that's only significantly true of reality television. But regardless, the importance of ratings are reliant on how hard it is to reach a target audience, not how many of that target audience actually watches. That's why the 18-49 ratings are the ones everyone primarily uses. People 50+ don't even matter to advertisers in prime time. It's not that people 50+ don't buy anything, it's just generally thought they can be reached with anything. That's why Harry's Law won't get renewed when it brings in 12+ million viewers.
you are right that reality tv is a big factor, but women watch more dramas too. I think networks are trying to make sitcoms more female friendly (ie, shows like whitney and two broke girls) since they know how much women watch tv as a whole. Its an untapped market for sitcoms.
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