the same could be said of jazz, prog-rock, classical, most of the bill at Glastonbury and any number of other minority-interest musics

Not true. Those idioms are born of the bourgeois social elite. Not co-opted & reinvented by them on the backs of proletarian art & creativity, which is in any case diminished by notions of anonymity & traditionalism. Like I say - a case of not seeing the trees for the wood.

Of course we can see the phenomenon of Prog in terms of it being a collective cultural tradition, but to really understand it's history & development, we have to address ourselves to the lives & times of the individual geniuses (specific musicians, bands, promoters, entrepreneurs, graphic artists, pharmacists etc.) that were involved in its creation, as oppose to its perception and definition. Prog, Jazz, Pop, Classical etc. are musics defined by the people who make it. Folk, OTOH, was a music defined by the people who perceived & collected it. A very crucial difference.

Talk about lazy generalisations, Brian - yours is positively narcoleptic.