You're all very gracious, thank you!
Armor makes you harder to hit for sure. It blocks the attack and protects your soft, smooth skin.
Erm, I do see the point you're trying to make. But in terms of imagining what happens it's often important to know the difference between being struck, even on the armor, and being missed. Blunt weapons don't have to touch your skin to kill you - imagine an armored knight standing with his back to a precipice and is attacked by an ogre with a big scary hammer. The knight probably has to parry or dodge to survive.
Of course, no RPG is going to handle every situation perfectly, and pointing out this one thing that D&D's rule system does badly doesn't by itself prove that it's awful. My main complaint about D&D's system is really that it's massive and complex, but still
leaves holes like these which are pretty well dealt with by simpler systems. Even Kobolds Ate My Baby
, an RPG contained in a 30 page black & white pamphlet, has armor reduce damage you take rather than making you hard to hit! (Incidently I didn't even remember that until just now; I was going to use KAMB to demonstrate that simple systems often take shortcuts with plausibility, but apparently not that shortcut!)
When TZH - the Mighty and Awesome RPG
finally comes out, I think it will be important to know whether an attack knocks a person back (possibly into a horde of crawlers) or actually breaks skin.