Why Do NPCs Never Run When They Are Losing?

This is just me ranting about one aspect of gaming that is not handled well. Retreating. Since the DM has no vested interest in the health of most NPCs, save a few “story critical” characters, the NPCs tend to fight to the death. I know this is because people enjoy combat. Sadly, if things go badly in the real world, real fighters run. They run screaming like little girls with their pigtails on fire. Mechanically, I know that older editions of D &D had morale checks that could send them running, but in 3.5 I do not ever remember seeing this function. Am I just overlooking it?

I think that all NPCs, save non-intelligent creatures should look at fleeing as a valid option. Add some bonuses/penalties for elite warriors or especially craven conscripts and have at it.

After all, as long as you hold the field at the end of the day, you are the victor.

Trask, the Last Tyromancer