Whoever said it, its a great quote! Makes total sense, which is probably why someone will want to argue about it!
It would be nice if it applied to folk. I don't want to get that discussion going here either, but I think that's a good explanation as well for a lot of the "folk-style" songs we talk about. Ashoken Farewell doesn't meet the purist definition, but it sure as hell 'sounds' like folk.