Does making a joke about something imply that there aren't “real” things to be said about it?
To put it differently: here, Knuth heard a popular song that seems to be just “That's the way uh huh uh huh I like it uh huh uh huh” repeated endlessly, found it funny, and wrote an elaborate joke culminating in that observation, hewing to the style of CS publications. Why does that make you sad? It's not as if someone's bit of humour has prevented others from saying “real things”.