My family is not upper middle class but if you try to pay for everyone, you'll find someone else has already slipped their card to the waiter. I've seen relatives almost get into arguments because two people insisted on paying.

Outside of my family, I've also had friends from relatively poor backgrounds insist on paying for lunch or drinks before. And I've had wealthy friends act extremely petty down to the penny. So overall I've found it's hard or impossible to generalize too much.