Your armor should loose condition according to how you take damage. Say you fall down a 10 block hole, instead of distributing the blow throughout all your armor, the damage should be blocked only by your shoes. Or your tunic should only be damaged if you are hit by a zombie.
Here is a visual example:
Falling down a 10 block hole in the game:
How it should be falling 10 blocks:
I suggested this same thing a while back because each piece of armor receives all type of damage. Though, each armor has their own durability.
No, all of your armor divides the damage equally, no matter how you get hurt.