I don't know what protocol is, but I don't feel you are obligated to get the newlyweds anything else. Sounds more like they were inviting people (everyone on their old and new contact lists) for numbers, which ultimately means gifts. That may sound hateful, but that's what it sounds like to me. The gift giving is between you and the daughter, not you and the parents. If the parents are reacting to what you did or didn't do, they are in the wrong place. Unless you are trying to have a closer relationship, just smile at them in passing and be on your way.