Couple of questions asked that have been missed.
I dont think dwarf skill relates to where the attack will land, the RNG decides location (fairly sure its what would be the easiest hit if you were adventurer). Dwarf skill then comes in for the hit vs dodge/block stuff. If you see combat reports where a creature is taking all shots to the head then it is unconcious or otherwise trapped (web, pain, sleep etc), KO'd enemies are always simple strike to any location and everyone auto-hits head. The guy asking this mentioned his iron axe bouncing off iron helm, this is a demonstration of why anything iron or below is kinda lame for edged weapons, a slash wont penetrate equal metal.
Layering clothing/leather under metal does provide added protection...albeit meagre. This can be seen if you set a dwarf up with metal plate and clothing underneath and hit him with a blunt weapon. The combat report reads 'bruised whatever through the *clothing here*' since the blunt weapon ignores the metal. (it actually hits the metal and the armor then hits the dwarf with a blunt attack, leather/clothing give when struck unlike metal, which is why they provide protection to blunt where plate doesnt.)
Someone else mentioned dwarves with odd remnants of clothing on along with armor, this is fairly common if you dont set the uniform to replace civilian clothes and can also cause some conflicts (I cant wear a breastplate, im wearing a rat fur vest!)