The problem with "the party should run" is frequently the party cannot run. As in they can run, but the foe can run as fast as they can, or faster. Like your Dragon example. How do you run from a dragon? They fly 80 feet in a single move. The party can run away at 60 feet a round taking no attacks, while the Dragon can keep ahead of the party while still making attacks. So...it's worse than staying and fighting. They cannot actually run away if the dragon wants to pursue...and why wouldn't the dragon want to pursue someone who just tried to kill them and who is on the ropes?
I've played a lot of games and I don't know of any off the top of my head where fleeing is a valid tactic for a typical encounter, especially at a point where you know you should be fleeing. I've had a few GURPS characters who could do it, but the rest of the party would still be screwed. The one exception is most supers games, depending on the characters.