Following on from my previous post, which mentioned just 3 clubs that I go to, there are perhaps more opportunities for "floor singers" in some of the other clubs around here, that have session nights for 3 out of 4 nights, and guest nights on the 4th. There are some among those that never come to the guest nights (mainly because they want to sing or play themselves), whereas others who support both (as they don't mind listening to professional guests!)
So, each club is on fact run in different ways, and each has its afficionados: some people prefer one format, other another, but all of them are, on the whole, well attended and much enjoyed.
Personally, I enjoy them all, and am flexible enough to do so and not worry about - "fings ain't wot they used to be" - as Will Fly said, accept that change happens.