All I would add to your wonderful piece McGrath 27 Apr 04 - 10:36 AM
is, that with a written piece ,there is uncertainty at the time of writing , first time of performance , and maybe after a couple of more performances the writer may feel the need to "tweak" some parts of the song.
If someone feels they have to "tweak" the song or tune in order to learn it / to suit their limitations or capabilities - I as a song writer will not be unduly upset, providing the person who is singing my song , has his/her heart in the right place" - and I haven't found anyone who didn't.
Interpretation of a song is a slightly different thing, and I have only once fell victim to someone who did'nt understand that the "Song" was a happy nostalgic song and not a reflective dirge.