I always found it a little dumb that ranged weapons don't allow flanking. Threatening I can understand, because it takes longer for a projectile to hit a target than it does to swing a melee weapon (for the sake of AoOs). But having an archer filling you with arrows from one side and somebody trying to stab you from the other seems generally "distracting" enough that flanking bonuses should be present.
Originally Posted by Greyfeld
At the same time, as someone who's done (simulated via Amtgard) melee combat IRL, I can tell you that it's actually quite different... there really is no "dodging" an arrow or thrown weapon, since if it's going fast enough to do damage, it's generally going fast enough you won't have time to get out of the way without completely throwing yourself out of the way (and likely not even then, especially for arrows), leaving you lying on the ground and ready to get shot more unless you found cover. Therefore, it isn't really the same type of distraction as it is for actual melee flanking, wherein you're trying to pay equal attention to both sides of yourself due to attempting to defend yourself against attacks from both sides (since you have the potential to do so, if less effectively). Ranged attacks, you're not distracted trying to defend yourself, because you really can't... the best you can do is hunt for cover.
Even if you have a shield, the best you can do is put your shield on the side of the archer, which pretty much guarantees you're leaving your back wide open to the melee combatant... and they generally don't have rules for such combat minutia in most pen-and-paper RPGs.