I had been wondering myself about the melting down, or rather non-melting down of the U.S. currency for a while as I had occasionally read a post by someone mentioning they had found an old coin dating early 20th-C in the change they had been given (?!)
I was slightly taken aback by this as we have a habit of taking in old or outdated coins and melting them down over here in the UK. Looks like people dig into their grandpa's old cash storage now and then and spend the little old coins at the local shop, which ends up being given by the cashier to a certain person who happens to be a collector, or it is otherwise just re-spent until it ends up in the pocket of someone who will cherish it more..