Conversations on G+ led me to think some more about this recent post about the abstraction of D&D combat in general.
Older editions may have changed the game, but it's important to remember that the D&D combat rules evolved in a context of a 1 minute combat round: in OD&D and AD&D 1st edition, the combat round is a minute in length. This is quite deliberate - and I am sure that most readers of this blog will be aware of the famous idea of Gary Gygax's that a D&D fight should resemble the sword fight between Robin Hood and Sir Guy of Gisborne in the Errol Flynn iteration. (For further information on that, see this en world post.)
Once you accept this notion - that the combat round is long and what goes on in it is necessarily rather abstract - D&D's combat system does make a sort of sense. Not perfect sense, but a sort of sense. The 'to hit' roll is a misnomer: you're not rolling to hit. You're rolling to see if, over the course of 1 minute, you manage to wear down your opponent's defences, either through actual physical damage or moral 'damage' or exhaustion or whatever. The opponent's armour impacts on your ability to do this, which is why AC is essentially a penalty applied to the 'to hit' roll, rather than a damage reduction effect. Your hit points represent you capacity to stay in the fight, which slowly gets reduced over time (the higher your level, the longer this takes). And your movement rate, which seems absurdly slow, represents the fact that you are scooting around and manoeuvring for position while avoiding blows, missile attacks, what have you.
The only thing that seems strange in this paradigm is missile attacks - why only one or two shots over the course of a minute? Even this, however, has a kind of logic to it if you think about it: it is surely very difficult to hit a moving target, who knows that you are shooting at him, with a bow. Especially at range, where he can watch the path of the arrow and just step away or check his movement. The fact that only one or two shots are permitted in a 1 minute round indicates that the archer is waiting to pick his moment to fire.
Once you've accepted that there is a certain logic to all of this, and that D&D combat is not really tied to anything particularly concrete, I would question why there really needs to be even an arbitrary length to a combat round of 1 minute. What is the purpose of a combat round? It gives a chance for everybody to decide what they want to do and then act. On that basis I would prefer the following definition: a combat round is how long the time it takes before somebody next makes a decision to do something different to what they are currently doing. This could be 10 seconds. It could be a minute. It could be 5 seconds. It could be 40. It doesn't matter: there is no credibility to stretch because we are not dealing with a system which has to make sense in the way that a less abstract one does. We are not rolling dice 'to hit', despite the name: we are rolling to see how far we attrit (that is a word: I looked it up) the opponent. "Rolling to attrit" has less of a ring to it, but that is the core of the D&D system.
Another good reason for preferring abstract combat is just that realism may be something of a fool's errand. I think that there is a kind of Western Martial Arts mafia that is slowly taking over these sorts of discussions online. I really like the idea of Western Martial Arts but I'm not persuaded that they are entirely realistic; until people start actually fighting to the death using these techniques, and agreeing that if they are injured they will only use medical techniques that were in use in the 14th century, I think that "what happens in a real sword fight" is still a matter of considerable conjecture and will likely remain so. That doesn't mean I don't like messing around with that sort of thing, as I did here and here. It just means that I don't think we lack justification for saying that a D&D combat round is an indefinite length of time, and that doesn't matter because nobody really knows what would go on in a combat round anyway.