The OP is referring to the fact you cannot see NPCs' eyes when they have the "helmet" on.
In reality, the helmet mesh replaces the head mesh when any NPC has the ebony or steel played helmet on.
Exactly, but why do they have to do this? Most of the helmets still let you see the character's face when you are wearing them.
Example, Daedric armor
[img]http://images3.wikia.nocookie.net/__cb20111117020422/elderscrolls/images/d/dd/Skyrim_Daedric_Armour.jpg[/img]
Some sort of black cloth apparently covering the face.
Compare with Dragon Bone
[img]http://images2.wikia.nocookie.net/__cb20111112022650/elderscrolls/images/thumb/c/ca/Dragonarmor.jpg/216px-Dragonarmor.jpg[/img]
You can see the the face under the helmet.