I thought the purpose of copyright was to keep someone from claiming credit to a song that someone else wrote? Rick, you say that it's a question of ethics, but isn't there a legal question there also?
One interesting note... I just got a CD over the weekend of some blues artists doing versions of songs that Led Zeppelin did. Only instead of crediting the usual Page/Plant, they credited the person who actually wrote the song. So Willie Dixon finally got credit for Whole Lotta Love.