Tom, first of all let me say that I agree with what you are saying. In particular, I agree there is no reason why the musicians shouldn't help the landlord to negotiate with the PRS, and indeed to contribute to the costs, which on a per session basis isn't much. However, I know from my own experience that an aggressive approach by PRS can be sufficient for a pub landlord to decide that he wants to have nothing more to do with them. And while the musicians may be happy to put into a weekly whip-round, the landlord will probably have to pay the full yearly amount up-front.

I would also like to pick you up on a couple of other points:

So far as your own income from PRS is concerned, I would hazard a guess that most of this comes from either your own performances or other musicians' cover versions performed at formal events, and notified to PRS via the small gigs and clubs scheme. However if I were to perform one of your songs at an informal session, I would be very surprised if you were to receive anything, because the PRS would be unlikely to learn about it.

On the question of attribution, I agree with you that ideally one should do this, and I try to do so when I can. However a lot of my material, particularly tunes, is stuff I have picked up by ear from playing it in sessions. I often don't know the title (perhaps the person I got if from didn't either). Even where I do know the title, it can be difficult to identify a composer, and songs and tunes are often incorrectly attributed to "trad" on albums or the internet. The ISWC database lists titles but there is no way of knowing whether this is the same piece of music, as scores or soundfiles are not included. In practice it can be very difficult to know whether a piece is copyright or not, or who composed it.