Actually, this would not be too hard to implement. The chance of armour taking damage when hit, and the amount of the damage, could be partially dependent on the durability of the armour. Damage taken could also depend on your health (slapping someone on the back would do more damage to a person with a broken rib than a healthy person).
The 'problem' would be in adding a few more variables that would need to be balanced (to be somewhat realistic, but not to the detriment of game play). It would have to be something noticeable, where you can tell your equipment is not performing as well, but not enough to have you teleporting back to town every 10 minutes for repairs, etc.