Thanks MTed for your contribution. I would remark something of your phrases:
"singers can learn most, or all of their craft by intuition and osmosis(even "classical" singers!!), and this is is often a great drawback for them, since they often lack the technical understanding of what they are doing that most other instrumentalists have--and this limits their ability to grow and develop--
I agree on everything except about classical singers. I don't want to mean they are more responsible or serious than others, but simply that classical singers had made THE contact with their instrument. Once they have learnt where the notes are, how they sound, how the instrument plays smoothly without being hurt, then they can face the aria Celeste Aida, or A Closer Walk With Thee. Of course the latter will never sound as the aria (this will be a disrespect to the nature of the song) but the singer will KNOW how to sing it. Wether he/she has the ART to sing, it is another matter.
Un abrazo (a hug) - Andrés