i dont think it is rude i think it is cheap of them.
Like others have said it doesnt cost much for a packet of chips and a few party things like fairy bread and cup cakes.
We r having a huge party for DD's birthday and we r supplying everything but alcohol.
i would not think to ask people to bring a plate and when you do ask you always end up with 5 of one thing that no one really eats anyways lol.

I say take presents and no food. if you get a complaint just blame it on hubby for forgetting lol