And then he pulls others up for grammar...
I'm not sure the chinese, indian or potato shop comparison helps here.
You know what you want and whilst delighted if it is slightly different, a chow mein is something you know even if the word is apparently just Cantonese for scraps.
Folk means something different to me, you, M'Unlearned friend, (not fair really, I am finding his medication is working as I keep ruddy well agreeing with some of what he says, only some mind...) and our take, based on mainly nostalgia shapes what we like. Now.. Like many "movements" it is evolving and some may not like that. Fine, but it doesn't mean you are right and others are wrong.
Jimmy Page is indeed a fine guitarist and when Led Zeppelin were playing traditional song it would not be easy to say they weren't a folk act during that song, especially if Sandy Denny was up there with them. If D'yerMake 'er sounds like reggae then they may not have been Bob Marley but playing reggae beats makes it as much a reggae song as a rock song. After all, they are all ways to describe a musical set of sounds designed to appeal to a certain audience.
One way to bugger up this discussion is to see how iTunes guesses genre.