I really have no idea when I first encountered the idea of having the quality of the Combat or "To Hit" roll establish the damage inflicted. I don't think I saw the idea during my first gaming period (1981-1990), so it must have been sometime after my return (2004). Of course, many gamers had long felt that the quality of the roll ought to matter...somehow. The most common reaction became the multifarious "critical hit" mechanics, but that is really only a half-step (if that).
Whatever the first such implementation, the game-system that has most impressed me in this regard is the Prose Descriptive Qualities (PDQ) system by Chad Underkoffler. I recently wrote about my regard for the game Truth & Justice (which uses PDQ) and how it helped me to understand the abstract nature of D&D combat. Combat (indeed, any sort of conflict) in PDQ is handled by having the participants roll 2D6+ relevant modifiers and comparing the result. If the attacker has the higher roll, he inflicts damage equal to the amount by which he exceeded the defense roll. If the attacker rolls 10 and the defender rolls 7, then the attackers inflicts 3 ranks of damage. Very clean.
Now there really isn't any "Rule of Ideal Game Design" requiring the quality of the one to affect the other. It's perfectly reasonable to have a mechanic such as D&D's, saying that the first roll simply establishes whether or not damage accrues and that the Damage Roll independently determines the amount. This is absolutely fine game design. No, the problem isn't one of design, but of psychology. I have never yet seen a player, told that he has to roll better than "9", roll an "18" and not excitedly point at a miniature, the dice, or a pizza slice, shouting, "Oh yeah! Nailed 'im!" And I have never yet seen a player in that same situation who, upon rolling a "1" for damage, not look rather murderously at the Referee.
Thus, I have been idly playing with the idea that the Combat Roll is the major determinant of the damage inflicted. Whether this is actually a good idea or not, I'll leave to your judgment, o discerning reader. I'm just conducting a Gedankenexperiment here.
First, it's obvious that I can't just swipe the PDQ method without entirely rewriting the combat system. That might be great and may be the subject of another experiment, but that's not what I'm going for here. So, no opposed rolls.
Second, as my loyal, imaginary readers know, Spellcraft & Swordplay is my D&D game of choice right now. This game works on the premise that the default, Chainmail combat system of 2D6 is never replaced by the "Alternate Combat System" using the D20. This significantly affects the experiment's applicability to most iterations of the game. But it also suggests something nifty to me.
One quirk of S&S is that almost all rolls are made by trying to get 11+ on 2D6. But not combat. Combat works by cross-referencing weapon type to armour class to determine a target number. Of course, non-amnesiac readers will recall my heroic battles with the Combat Matrix to come up with a preferred version. And, as it ended up, I decided that it was easier to drop the idea of having the matrix determine the target number and instead determine a modifier with the target number standardized at 11+ (like everything else).
What a happy occurrence! Because it immediately suggests a mechanic: let the number in the one's place determine damage. A roll of "11" does 1 point of damage; a roll of "18" does 8. I like that. It's dead-easy to remember and it means that the more skilled warriors do more damage, whether they have a +9 Sword of Bad-Asssery or just a pruning knife. That definitely fits in with the abstract nature of Hit Points and combat in general.
Now it gets a little bit more complicated. S&S dispenses with differing weapons doing differing ranges of damage: everything is 1D6. Differences among weapons are handled by how they interact with the various armour classes. Up to a point. Because that same psychology that inspired this post--the one that wants the quality of the combat roll to affect the damage--also wants to see some difference in damage between a dagger and a claymore. In a variable weapon system, that's easily handled, but not in this experiment.
Hmn, I suppose the easiest (if not cleverest) thing would be to give a damage bonus to large or two-handed weapons (say +2) and a subtraction to small weapons (say -2).
So, we roll 2D6+modifiers and, if we get a two-digit result, the one's digit tells us how much damage we do, as modified then by weapon size, strength bonus, magical bonus, etc.
Well, it's an interesting idea anyway.