"The term 'folk music, for me, is a generic one, covering a multitude of sins."
At last, we agree on something. If that is what you have been saying all along, I apologize for not recognizing it.

"we had a long thread on Mudcat recently about an event in the US North-East, much bigger than any I've ever attended, which the thread initiator described as a "Not Folk" festival. It had the same sort of exclusivity I'm talking about"
I agree with you, that sort of exclusivity is not right. The promoters of the festival are doing a disservice, yet I still feel they can call themselves "folk".   That particular festival is making a huge mistake.

"Most people who learn DenverDylanPrine stuff never take that additional step. "
I agree. It is their loss. It is also a loss when DenverDylanPrine material is not learned (at least Dylan and Prine), but that is an individual choice and their loss.