@SpatzieLover, I think this might be one of those regional/cultural things. In my upbringing, there was a clear division between guests and hosts. The hosts entertained, supplied the food, served, etc., and the guests allowed them to do that. Unless an event was explicitly designated a potluck, no one brought food or beverages—the hosts controlled the menu, chose and prepared all dishes, and decided how and when they were served.
When I arrived in California, I was surprised to find that guests routinely bring something to add to the table. I’m still ill at ease with this. When I’m the guest, I don’t expect to do the cooking. When I’m the host, I don’t really want others in my kitchen, nor do I want to be forced to incorporate into the menu something that may or may not compliment what I have planned. I’m especially put out when I have prepared something that is preempted by something someone has brought—say, a dessert that they expect to see served in place of the one I have prepared.
As a guest I’m not entirely comfortable with the “après-vous” “no, après-vous” routine of negotiation: “Can I bring something?” “No, nothing—just come” (but you must bring something anyway—which you have to guess at blindly because the hosts have withheld any sort of hints, and you mustn’t show up empty-handed).
I think there may be many variations on these customs among different ethnic groups, within vs. outside the family, etc., and they all make me uncomfortable because it seems hard to avoid being wrong. One of the down sides of a heterogeneous society.