I'm not an American, but I am used to being able to modify an order. I don't think of this as being entitled as I am after all paying for the meal and depending on the restaurant it's not exactly a cheap meal. That being the case I don't see any reason for negotiation if I'm not happy with the meal. The only thing I'd agree with is that it'd be absurd to request another meal for free simply because the one you chose wasn't to your fancy.
The customer is always right attitude is one that I appreciate Americans having. While not as bad in Australia as some parts of Europe, the attitude here is definitely closer to "give me your money and and leave" than "what can I do to ensure you leave happy?"