One of the problems with defining folk music as 'that which is played in Designated Folk Contexts'...

The point of which is to at least try and accomodate the diverse musical styles that occur in these contexts under the general heading of Folk but which might not be considered Folk in the strictest sense of the word. In other words, it's an empirical definition based on a lifetime's ongoing evidence & near nervous breakdown. Also it attempted to understand, and appreciate, why this might be, though in the end I give up. Here in the North West Folk Music is that which is by and beloved of Folkies, on the evidence of which I'd say (in the last year) a good 85% of which could be performed as pop / rock / easy listening in any other context irrespective of Form or Derivation.

...is that it denies every other nation of the globe (apart from a few former colonies) the right to their own folk music.

From an enthnomusicological perspective context is just as much a consideration as form / derivation. Otherwise when I said Surely Folk is as much about form as it is derivation... I was talking specifically about English Speaking Folk Song & Ballad. Sorry for not making this clear. But whatever the music, whatever the culture, Form is just as important as Derivation which almost brings me back to the Equine Truism, but perhaps that particular beast has long since bolted. Let's leave the stable door ajar shall we?