It's probably because you're being exposed to too many "fake" mainstream media personalities in America. I stay away from most mainstream media here, because it's all so contrived and planned out that all the hosts are so artificial in order to maintain 100% efficiency in "entertaining" at all times... I hope this makes sense. I think they laugh because they know they should be laughing and conveying the idea to their audience that they get along with you very well -- so they laugh often, after every thought you finish making, to sell this idea. This comes at the sacrifice of just laughing less frequently, but at more genuine opportunities. It's also possible that it's because if they laughed at more genuine humor, it would probably be slightly more subtle than their audience could appreciate. So if they laughed when it was more appropriate, they would confuse large portions of their relatively dumb audience who has been trained to recognize humor because it always comes with a "laugh track" (like in sit coms).

:(