Since the traditional "to hit" and "damage" rolls have been combined in the ARG system, the temptation here is to make armor one more modifier to the weapon skill roll. Although this would simplify things a bit, it is still not a good idea.
Consider this: If a defender were wearing plate armor which reduce his chance of getting hit by 8 points, how much real damage did that armor stop? If he were attacked by a club, those 8 points would equal only 3 damage points stopped. If he were attacked by a two-handed sword, then 8 damage points would be stopped. In other words, clubs are better able to penetrate plate armor than two-handed swords! This, obviously, will not do! The problem is that if you subtract the armor's defensive ability from the weapon skill roll before calculating the weapon's damage multiplier, then it would result in proportional absorption of damage.