There's this cool trade off between how much you can charge for commercials, and for how long you can take up an audiences interest. The cable shows have longer intros. I think this is because of how expensive it is to shoot the footage, but they know they can capture the audience for a full hour, so they'll grab any way to get to that full hour cheaper.

Cartoons are an extreme example, being very very expensive to animate, many cartoons in Japan have an intro of almost 15 minutes, then ~25 show, then 5 minutes outro! (these are cartoons targeted at teens/adults)