Bob Knight's comparison goes to the heart of the matter. No one is ever satisfied with what they wrote. The true artist is his own harshest critic, and there's always a better way of saying what you wanted to say. Even if your thinking hasn't changed a bit in the meantime.

Since if it's worth anything at all, a song is (at least partly) a message- conveying an idea- the effectiveness of the song lies in how well the idea is conveyed, not how well the actual word sequence is preserved.

So listeners almost inevitably change the words to match their interpretation of the idea. It's this that drives the folk process- mutations are seldom random and sometimes totally beneficial. So don't get too uptight about changing the words, if the sense is maintained.

On the other hand, pure garblings by professionals illustrate the premium these often place on presentation and slickness over content. And the fact that these garbled versions often get the greatest circulation shows that their strategy pays.

Music doesn't always benefit from "an injection of quality", unless quality has a wider meaning than being in tune and playing the right chords.