I would argue that it's about bringing out the rediculous of normal social things and then amplify that on the punchline. You take a social thing, deconstruct it, and then reconstruct it in such a way that the result is hilarious. The building process itself should get laughs, and then the biggest laugh on completing the picture (punchline.) A skilled performer can keep you smiling just in anticipation (as you might be smiling as your friend is telling you a joke, knowing the punchline is coming.) Norm might be one of the greatest joke tellers I have ever observed.

As to the writing, I feel that you should be a great thinker to be a great joke creator. Maybe not all comics need to actually write jokes. But writing in general is a creative process, which is also thinking. And writing jokes gives you material for remixing. I agree it's mostly performance though. Some comics are all performance and little to no dialogue.