cave-ins, atom smashers, freezing and obsidianizing are also insta-kills, but they ignore the damage system.
These are all good fun when you manage to employ them in traps, but usually these kinds of deaths are not something you will see during a normal combat when some of your dwarfs bump into something hostile and you have to call out your militia.
I must admit I take much enjoyment from reading the combat log and will regularly pause to look at the blow by blow combat description. Its one of those things that make DF unique and superior to many expensive AAA titles.
But once you have read a lot of combat logs you will notice that jamming bone into the brain is the way most things die in DF. I believe that during the history of man up until the advent of firearms most people that died on the battlefield did not die from trauma to the brain, but due to blood loss caused by stabs from sword and spears. Many wounds would not be serious or fatal by themselves but blood loss from several and exhaustion caused from battle could make anyone loose consciousness. Given the medical sciences of the day recovery rate was slim even if you where lucky and your side won and was able to get you to safety.
That is not to say that 1 hit kills didn't happen in the old days as I am sure quite a few got a spear through the eye or got slashed in the neck leading to rapid death, but most would protect their vitals as good as they could.
I was thinking the other day if it could be interesting if creatures could go unconscious in DF when tired and their blood level/blood pressure got low. As of now creatures only go unconscious due to pain or extreme tiredness and they often awaken pretty fast. lets also say that the dwarfs and the creatures don't automatically know if an opponent is actually dead or unconscious. It could lead to battles where fighters that that have been wounded and have gone unconscious are left for dead and are not automatically finished off by an enemy. That way a dwarf may be incapacitated and later rescued by your doctors before taking lethal damage. On the other side Goblins and other creatures that you thought where dead may awaken and try to crawl off the map slowly leaving a blood trail. This would make policing the battlefield/winning the fight more important as it would allow you to recover wounded dwarfs and kill off wounded enemy.
Well, enough rambling from me. I sometimes find it hard to contain my passion for DF