The dev blog mentions that Toady plans to implement aimed attacks so we can go for a specific body part with attacks besides wrestling, but I think he needs to implement aimed blocking (as in protecting certain parts of yourself) at the same time.
My reasoning is that armor would otherwise become much less useful, especially without the as-close-to-full coverage you can currently get (covering everything but throat, ears, nose, fingers, lips and teeth).
Being just partially armored in real life is useful because it limits the places most enemies can successful attack, letting you apply more attention to actively defending your body parts not armored or get by with less attention. For example, if you wear armor on your back enemies have to attack from your front where you can parry their attacks; if you armor your legs you could get away with a buckler instead of a full shield making it easier to attack with your hands.
However, if there's a way to focus attacking into single body parts while defending is still "spread out" amongst the body armor loses a great deal of its function. A unit shouldn't be putting the same effort into guarding a chest wearing masterwork adamantine breastplate as a lower body with nothing but a tattered rhesus macaque leather loincloth.