Chris, I read your last post after I had made my last one.

Your point about considering the question from the standpoint of the SONG itself is an excellent one. In a way, you're expressing - much more poignantly - what I was trying to say about some songs really needing multiple voices, harmonies, etc.

If someone decided to turn my song "Harmony: One, Out Of Many" into a solo piece, it would be kind of a musical oxymoron, as the theme is unity in diversity and the one repeated line is "let the music be sung, not in unison, but harmony."    Having one person sing that song makes about as much sing as belting out "Silent Night" at the top of your lungs.   There are many songs that really do call for multiple voices -- and not just on the chorus, if one exists.