This came up in one of the "Cars" episodes: I think Sarah Jessica Parker. When you're famous, and everyone knows you're rich, you should tip big. Why leave people with a bad impression? Jerry Seinfeld and Sarah Jessica Parker were at the place where I work. What did they tip? What answer do you want her to give? Sarah has some formula, percentages, Jerry says never mind all that, throws in some cash and Sarah is impressed.
Here he is with some New Zealander. How much do you tip? 20%? More? Jerry: 20%? That's how much you should tip. I have to tip much more. Q: How much? 50%? Jerry: I don't know, a hundred percent? You want this person to remember a famous person was here, he was generous. Interviewer: You know in New Zealand we don't really tip. Jerry: Well, that's going to change, because I'm going there, and I'm going to tip big.
A typical American combination of generosity and disregard for local ways.
"Why do Americans now rely more on comedians for political commentary than on journalists?" Jerry: they have lost confidence in journalists. If some joke gets a big laugh, this makes it seem "we all agree," and this in turn makes it seem the implied view is probably true.