I think that, when it's time to have a dance, people have always played their music on whatever instrument they have available and know how to play. I don't think the skill level or training of the musicians, or whether or not the accompaniment is "arranged", really has much to do with it. I also don't have the idea that piano players are somehow "trained" and others aren't. I've been playing the piano all my life and used to get paid a lot of money to do so, and I'm self-taught.