Even Mordell's "terrorist" humor (which I found to not be very funny, not only because it's not a good time to tell terrorist jokes, but the material just wasn't funny) is an exampleI actually disagree with your statement above. I find that the best comedians can joke about serious topics and situations in a way that can bring some really great perspective.
Two good examples of this are Carlos Mencia and Phil Hendrie (I don't know if anyone listens to him, absolutely hysterical)
I recommend going to see Carlos Mencia if he is playing in your hometown, he has a way of poking fun at every type of person, from every type of culture, current events and bringing it all together in the end. (Definitely an "R" rated show though - not for the kiddies)
Anyway - just my two cents . . .