I have noticed that newspaper cartoonists often use variations on the same gag on any given day. For example, the other day, Dilbert and F minus ran variations on a joke involving consultants shooting themselves in the foot.
Dogbert is probably right… the people that would buy that book would do so without stopping to engage in Dilbert’s circular reasoning.
I don’t mind the cartoonists using the same gag, as long as they each have their own take on it. In fact, the only comic I don’t like at all is “Red and Rover”. It’s just some sad, lonely kid whose only companion is his dog. Depressing!