I think you're noticing it because you've been away from TV for a while. 20 minutes for a half-hour show is pretty standard "show time". It is getting so I wonder how sitcom writers can tell a story in that short amount.
When hubby and I take a "TV vacation", we're amazed by not only the commercials but the content of the programming and commercials when we get back. There is so much JUNK on TV. When it comes down to it, there are only a few channels we want to watch and even those have gotten cluttered with useless programs. The other night hubby was watching "Ice Road Truckers" while I was in another part of the house doing something else. DD came in because she didn't want to be in the living room with dad. She complained, "He is watching Ice Road Truckers again. It is trucks on ice. It is supposed to be scary but it really dull. How many times can you see a truck driving on ice? I get it already." LOL - she is right!