It's easy to get pious about stuff like this. One possible effect of quoting origins not just of song but of arrangements, players etc is to show off how wonderfully knowledgeable you are compared to the plebs in the audience.

I try, often in vain, to stick to the rule of saying something to the audience if I think it will interest them, or add to their enjoyment of the song.

If people really like something they will often ask where I got a song and I will tell them at great length, if they dont then i dont suppose I would be doing the originator any favours by claiming my efforts were their arrangement.