In your example the enemies with ranged weapons fire away while the others chase the PCs. Now when the PCs turn around they can gang up on the melees that followed them while the archers suffer heavy penalties. The PCs can also more easily use magic or items to separate the enemy force
Players also fear that their characters die, so is it the systems fault that the PCs can take damage?
When the PCs do not use a option, especially one which is so easy to use or has such a low cost then the only one at fault are the players.
The system should not need to cater to players without even a basic grasp of tactics or chances in order for something to be viable.
I think just about everybody else is saying that running away in D&D is NOT easy to use and does not APPEAR to have a low cost. it may just be a perception problem, but perception is reality for most people.
And some of us think the system SHOULD cater to the kinds of activities that you want players to do. [MENTION=6673496]Rogue Agent[/MENTION] just posted an excellent article to that point.
I would also question, what else is the point of putting in a higher level monster except to entice the party to run away (or at least not fight)? It certainly isn't to fight it as the general lesson is you can't beat a sufficiently superior force. in fact, use of too strong of a force removes the validity Fighting from the 6 basic responses to an encounter. If the monster is also able to thwart running away (faster, teleporty, whatever) then that's another option that is removed from viability. ironically enough, certain encounters vaunted for their "look how open my world is" and in reality they restrict options. It is not valid debating to say "look at all your freedoms, you could kill yourself if you want to" when for most people, that's not a choice they would directly take (though their actions may get them killed, few people sign up for Direct Suicide).