Here in Florida having doors on or off is a variable dependent on your floor-sill.
Samurais and most Jeeps/Trucks have enough of a sill below the door such that if something falls on the floor, it will not be able to roll out of the vehicle. After talking to a local (florida again) police officer, he said the only concern about people running doorless is things rolling out of the vehicle at speeds and causing injury, accident, or otherwise. As said, the sills prevent this.