That all makes sense. I think another reason that Joni Mitchell's songs are not always good to pass on is that they are often too rhythmically and melodically complex to enter an oral tradition. In fact, following Joe's link and reading Sharyn's excellent "Wallflower Waltz", I'd say we have a more likely candidate there!
I have only heard one of khandu's songs, which has made me more impatient to hear his album...