I'm with Jim Carroll on this one.

I don't much care about the instruments being used, the venue, or the mode of delivery. If it comes from the folk process, it's a folk song. Steeleye Span rocking out on a folk song is still doing a folk song. Tracy Chapman singing a self-composed song -- even if the only accompaniment is acoustic -- is still singing a pop song.

There are big differences musically and lyrically, and they are (to me at least) very obvious. "Folk song" and "contemporary acoustic music" are very different genres.