"... It does not give them a get out once they have entered into a contract ..."
Actually that is exactly what it does.
Offering people a food buffet in no way, shape, or form. guarantees them the right to have no limits placed on their behavior.
And the right to refuse service is just that...if you act in such a way as to get yourself expelled from the establishment, guess what? You just had all you can eat.
If the restaurant should refuse service in an unreasonable manner, say according to race, or after one bite, then they would not be covered by that right to refuse...
And conversely, if the diner should act in an unreasonable manner, by causing a disturbance, or demanding more than is reasonable, or demanding to stay after the restaurant closes, then they lose the protection of the contract.
Bottom line, 'Buffet', and 'All you can eat', are not infinitely unlimited guarantees, in the case of a dispute, 'reasonable' is going to be the key word...judging by the commentary on this case, not too many people are finding it reasonable to eat so much food that no one else at the buffet has a chance to get any.