.. Would musicians belong to these two distinctions be ,for example, comfortable sitting next to each other on the same bill at a folk club?
Err .. not unless you're seriously odd. Being lazy I learned most of my stuff from singarounds & sessions. Ergo, most of what I play is wrong (as in theres bound to be a pedant about who'll say so).

Kudos to Brian - that's a scholarly dissertaion, excellent sense and no less than we might expect :)

As you'll gather Cristian, this is an excellent place for free advice - Fear Not, it's not always like this in here ....