I think it always depends on what is the norm with your group of friends. whenever we have a get together, we always divide up the meal so everyone brings something. That has been our way since the beginning.
I get why your annoyed though Blondie, If they are a couple who never contribute but always expect people to and that they have asked you to bring what sounds like the main part of a meal then I would be annoyed too. Could you maybe go buy some premarinated chicken wings and cook them there in the oven.