I feel sure you are right Frank. I guess most folkies would say you are. I think the problem is a bit like this: my 5 chords on the guitar won't be much use in another folk tradition if it is significantly different.

I have heard some Indian and some African tunes that sound a bit like jigs or reels but to join in with the chord progressions I have will almost certainly not work - not straight away anyway.

Brass Monkey have brought together different bits of English music but the level of musicianship is high and I don't see lots of BMs.