I think a lot of pop has its roots in folk but maybe that is just me. I like, for instance, Jethro Tull and find them quite folky at times. More up to date, I am not that keen on Mumford and Sons but can see the folk influence. A lot of the tunes are lifted directly from the tradition (Belfast Child by Simple Minds to name but one) As kids we regularly changed the lyrics of pop songs (Is there anything that you want? Fish and Chips! Is there anything I can do? Pass the salt!) Is that folk music? What about the traditions of other countries? Is it OK to have Country Music or Bhangra at folk clubs? As I keep saying, I don't have any definitive answers as I find the lines too blurred. All I can rely on is what sounds, to me, like folk music. As such I would never be one to try and define it!