When I were nobbut a young whippersnapper, most pubs had an old upright in the bar somewhere.
Its not folk/trad but I can remember singing along to " A Nightingale Sang In Berkeley Square" in a pub in Looe one night about twenty years ago.
I also had the great priviledge of listening to Tom Anderson, Aly Bain, and Violet Tulloch (on piano) at a ceilidh in Lerwick back in the seventies.
In my opinion they could get rid of the big screen telly's in pubs and bring back the piano. Nothing kills a social gathering more than the goggle box.
Unfortunately, the telly is in and the piano seems to be out! (Well around here anyways)
A great variety of instruments are used for folk/trad tunes/songs the use of one or many can add (and occasionally detract) to the richness and blend of either.
That said what I really think matters here is that the music is played and the song is sung.
To be honest, I'd rather listen to someone in a pub banging out "My Old Man Said Follow The Van" or in fact anything else, than watch football anyday.
Thanks also for the links to Mairead Nesbitt and Lisa Kelly. Crackin!