If the delivery, instrumentation and style are identical one has to ask what this quantitive difference is?

I'll answer that one by echoing Howard:

Traditional folk is performed unaccompanied, with accepted "folk" instruments such as guitar or concertina, with electric or electronic instruments, or with an orchestra. Performing a traditional song in a non-folky way doesn't make it any less of a traditional song, so why should performing a composed song in a folky way necessarily make it "folk"?

Personally I'm not talking about what individual pieces of music sound like. Unaccompanied folk, acoustic guitar folk, concertina folk, laptop folk, drum and bass folk, string quartet folk, death metal folk - it's all folk music if the song is a folksong to begin with. And if not, not.

If you're not an enthusiast for traditional music (and you sound fairly dismissive of the idea of being an enthusiast), then you probably aren't bothered about how much traditional music people are able to hear. I am, and I would really like to hear more folksongs in folk clubs. There are lots of acoustic clubs and singer-songwriter clubs and open mic clubs where folk music is treated as just another speciality, and a slightly quaint one at that ("and here's Pip, who I expect will give us something traditional"). I don't object to those clubs - I've been at some great nights of assorted vernacular creativity and artistic imperfection. But I do object to being told that a completely undefined and open-ended mishmash of material, from Dylan to Rudyard Kipling to free improv, is in some mysterious way the definition of folk.