I've never heard of someone getting paid for this. I would be very surprised to hear that it happened in the UK. The best I've seen is free beer or refreshments for the participants.

On the other hand what we sing and play is entirely our own choice. Ideally the session doesn't have a leader, but works well enough so that everybody gets a go. We're just happy that pubs allow us to meet and play, but don't advertise the session to the general public so that we're 'on show'. That gives us the freedom to try something new and not worry if it doesn't work. If people want to come in and listen, that's fine. It's better than hiding our music away where the general public can't get at it.

I'm sure that 'paid for' sessions are equally valuable. The more exposure we get for our music gets the better for all of us.