Originally Posted by PatrickWeekes
I personally like "unconscious 'til end of fight" because it lets developers take the gloves off. If a single special ability can kill a player and result in having to reload a game, those special abilities can make a fight too frustrating, and it has to be dumbed down. If a single special ability can kill a player until the end of combat, then you can expect a good fight to take down two-thirds of the party instead of "might get most party members into low hit points". It gives the combat designers a bit more slack to play with, and that usually results in combats that are more fun.