First rule I don't like

[KarinsDad]

I prefer a system of "all enemies are dead" unless they make a save. If the players want captives, they have to state so ahead of time and then the DC of the save changes (based on PCs pulling their punches in the fight).

As an example, the DC needed to survive is:

Minion: 20
Lt.: 16
BBEG: 12

A bonus of +4 (or so) to the roll is made if the players wanted to have a captive.

But, all damage is lethal for the most part. A system like this also allows the DM (without fudging) to determine that some NPC in a fight survived (if a potential desired game hook), but the PCs did not notice.

The artificial concept of the players deciding after the fact whether a mook survived or not just feels wrong. However, 4E has several "players make 'out of character or campaign metagaming' decisions instead of the DM doing so" type rules. 4E panders a bit to the "players should be entitled and empowered and key story decision makers beyond their PC" philosophy.

 

[Korgoth]

I suppose another way to do it would be this:

Strike to Subdue: Strikes to subdue inflict half damage. If the enemy is taken to 0 or less HP he is incapacitated rather than killed.

That's even simpler and it works. There's still the chance that you accidentally kill the person you're hoping to subdue, and there's a penalty for "nipping at the knees", but you can do it and there's very little extra math.