We just got back from WDW and one of the things we noticed was the "empty threats from parents" and the kids who obviously knew an empty threat when they heard one.
While we were waiting for the Spectromagic parade to begin we saw one 4 year old who had complete comtrol of her mom. She wanted this, she wanted that... mom said no, kid cried, mom said no, kid whined, mom made empty threat, kid whined some more (You get the idea). By the time the parade started, the kid had a spinning light toy (which she traded twice for a different one), a Minnie Mouse headband, a light saber sword, a stuffed animal, a book. And, 5 minutes before the parade began, the mom ran off and got popcorn and pop. The girl complained because SHE wanted a hot dog.
I've always been of the opinion that you need to keep your normal rules as much as possible. My youngest DD has a number of disabilities, but if we let her get away with bad behavior, that will be the real handicap. And, trust me, her behavior can be pretty bad if she thinks she can get away with it.