I would say that at the very least 90% of the music and songs I hear in folk clubs is folk music as I and most people (except Jim :-) ) consider it. Clubs that had a narrower booking policy based primarily around traditional song alone would not appeal to me and I suspect would significant narrow their potential audience base. The variety of music to be heard at clubs is their attraction to most I suspect. Jim keeps throwing up extreme comparisons but as has been said so many times on here the music most often heard at folk clubs (certainly those I have attended since the age of 17 - 43 years!) is folk music. Not jazz, not opera, not 'pop'. I've been to see a few blues players at folk clubs over the years and I booked an excellent Danishfolk /jazz fusion band but other than that almost everything else I have heard has been folk