Pits & Perils (P&P) treats armor differently, and this post aims to explain why and what we were thinking...
As gamers, we've grown accustomed to armor granting constant and uniform protection. However, there's little to suggest that this is actually true, and some evidence to the contrary.
We assume the following:
(1) Armor reduces the number of vulnerable spots, but cunning opponents will know where to find them, and even when armor is used, the wearer must still aggressively defend themselves.
(2) The benefits of armor worn diminish greatly over time. For instance, a wounded or fatigued fighter may become hobbled and slow, making it easier to slip a blade under a breastplate or into an exposed armpit, often fatally. Notice here that the attacker bypasses armor completely, and previous efforts to capture this have resulted in excessive book keeping.
Now, in our system...
Using Pits & Perils, all attacks require 9 or better on 2d6, although fighters and higher-level monsters get bonuses to reflect their skill and ferocity, where applicable. Armored foes are difficult to hit because they're so well-protected, but unarmored targets are equally hard because they can move faster and are better able to avoid blows in the first place, and this comes out in the wash as "9 or better" for all, subject to modifiers.
So what does armor do if it doesn't absorb damage and/or make you harder to hit? Simply put, armor prolongs life.
In P&P, armor adds bonus hits to the wearer, so a fighter in chainmail (+2), and shield (+1) would get +3 bonus hits, and since the average (melee) attack scores 1 point of damage, this goes a long way towards protecting the user. Bonus hits are lost in combat and recovered through magic (miracles) and/or rest because, ultimately, these represent the ability of the wearer, and this diminishes over time with fatigue and injury.
Armor protects the wearer to be certain, but it doesn't grant invulnerability, and the battlefields of Europe were littered with well-armored corpses. This is what we were thinking!