It excludes most "folk music" played and sung these days, as major (the major?) transmission mechanisms are recorded material, whether written or electronic.

I don't know why they needed the qualification of "popular" on music which has not been re- created. And if re- creation is a major criterion, most jazz, other than the strictest New Orleans variety, would qualify as folk. Unless of course you define "community" to exclude (jazz) musicians.

Or to put it another way, why bother trying to define a process as a static object?