I've never come across a 'strictly traditional' folk club in over 40 years as punter and performer, though I don't deny they may have existed back in the mists of time. What I have come across are folk clubs in which traditional or traditional-style songs are favoured by the organisers who make their preferences known through the performers they book, or by assembling a like-minded group of friends who like the same kind of thing. If the 'wrong' kind of singer turns up to do a spot then I hope they'd be treated with generosity. However I was told many times in my days of cold-calling organisers that such-and-such a club didn't like'that finger in the ear stuff' at my first mention of traditional songs, so prejudice clearly works both ways. I don't have a problem with that - if someone volunteers to put the work in to run a regular venue, they're entitled to put on whatever kind of music they want, as far as I'm concerned.