I agree that rugby songs and the like ARE the only true "folk songs" possible any more. The subcultures of ruggers, hash-house-harrier runners, etc., are among the very few contexts in the modern world wherein a true oral tradition can still be maintained.

The more conventional or respectable "folk traditions" rely on recordings, if not books, if not academic support and sanction, to maintain their existence. Not that there's anything wrong with that, but it is qualitatively different from the way these same traditions were created and maintained prior to the 20th century.