Death by Massive Damage

If ever there was a pointless rule in D&D, it is the death by massive damage. If you are capable of surviving the loss of 50 hit points in one blow, you're not going to fail a DC 15 Fortitude save. The rule was introduced to combat the tactic of escaping by jumping off a 200-foot drop, but it doesn't really do that.

Of course, the situation is somewhat different in other games. In Star Wars, a fall requires a Reflex save, or the damage applies to Wounds rather than Vitality, which is a rather more deadly matter. In Call of Cthulhu, the threshold for the save is 10 hit points, and it's entirely possible that a character can survive the loss but fail the save. In d20 Modern, the threshold is set at the character's Con score, which is much the same.

There's not really a point to all this, except for one small thing: the lethality of a game depends on more factors than just how many hit points the character has. By adjusting the damage threshold, the difficulty of the save, the attacks that can reach the threshold, or just means by which the character's hit points can be negated, the lethality can be tailored to your taste.

Of course, I still think the Vitality/Wounds split doesn't really work for Star Wars (to lethal), and the existing hit point system doesn't work for Call of Cthulhu (not lethal enough). But that's just me.