I think that the very-most-recent posting to that earlier (and now very long) discussion makes an excellent distinction, betewen "folksongs" and "folk music":

Subject: RE: What IS Folk Music?
From: GUEST, Mikefule - PM
Date: 16 Mar 07 - 01:20 PM
(Note the date and time; sooner or later, Mikefule's post will no longer appear at the bottom of the thread, as it does right now, as I begin writing this message.)

I'll paraphrase his suggestion: "Folk Music" can be defined by the spirit and intention of its participants ~ playing for personal enjoyment, community intercommunication, etc., while "Folk Songs" are those whose particular histories define them as belonging to certain recognized traditional folk cultures.

Songs that are not folk songs can become part of "folk music," as defined here, and indeed do so very often. Songs originally written for the popular commercial music biz become so well known that folks spontaneously adopt them for their communal enjoyment. Examples: "Over the Rainbow," many Beatles songs, etc.

On the other hand, recognized folksongs can be performed in a commercial or otherwise gussied-up, non-"folk" context, and thus fail to be part of "folk music" in that particular guise. Mikefule gives the excellent example of Thin Lizzy's version of "Whiskey in the Jar."