Total realism would never be achieved in any game.
However M&B is striving for a somewhat realistic gameplay. Having said that, I believe that whereas a certain level of realism should be present in any game, (more / less in some respectively) there is a sort of a 'rounding off' point of every little minor thing.
In current situation, I believe the creators attempted to have a specific use for 'blunt, piercing and slashing' items. Blunt, in this case, would knock somebody uncontious. Although it is true, blunt weapons CAN be very fatal, there is a much higher chance they would rather knock somebody out rather than kill. So it was a simple 'round off' to separate blunt weapons from the slashing and piercing weapons. (I think so at least)
Having a blunt weapon have a chance of killing an enemy, would not achieve any end result, other than a more variable chance of whether your foes perish or are held captive. Ultimately, if slashing weapons and such could knock out, and blunt weapons could kill, the difference between blunt and others would be nullified, thus actually reducing the gameplay variety. It would not enhance combat, improve gameplay, make the game more challenging, or provide any other benefit, and even realism is arguable at this point since the game is still realistic in terms of 'blunt would knock out somebody better than a slashing weapon'.
Zerck no offence, but your posts pissed a lot of people off, and if you DO want to achieve a certain point of realism in the game, you have succesfully done the opposite since people would be arguing against it in this thread thus slowing down the flow of useful suggestions. And I personally don't see why you are bothered by such a small and insignificant 'unrealistic' fact, whereas there are much more major ones which exist in the game. Perhaps you were suggesting on another way of capturing prisoners, without the need to fight but mis-placed your words?