Actions in D&D are bound to the game.
What does this even mean? The phrase "bound to the game" isn't an ordinary phrase of English (unless you've tied someone up to a gameboard or box!).
Consdier a typical dungeon scenario, in which the PCs confront a closed door. What are the possible actions the players may declare? Just as, in real life, the possible things I might do when confronted by a closed door have no practical limit (and perhaps no in principle limit, either), likewise in the game. The PCs can try and turn the door's handle. Lock (or unlock) its lock (if any). Listen at it. Drill a small hole thorugh it to spy through it. Peer through the keyhole (if any). Cut it down with an axe. Pour water under it. Etc. No edition of D&D has rules for resolving most of these options. There are rules for listening, and for bursting the door open by sheer strength, and that is it.
Yet the other options are all permisible moves for the players of those PCs.
For example, players are limited by what they can capably communicate to the DM.
I don't understand the point of this assertion. I am assuming that the players and referee are communicating in a natural language, most often (when it comes to D&D) in English. There is no upper limit on the number of well-formed sentences of English, so the requirement that the players must communicate their desired actions to the referee by way of a well-formed English sentence does not impose any meaningful limit on the range of possible actions.
1970s D&D players were mostly adults and part of the wargaming community.
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These were not people who played games so they could hand wave away the rules.
I don't see what this has to do with anything. The Forge, whom you criticise so much, don't play games so they can hand wave away the rules either! The most important underlying tenet of their design approach is to design rules that, when actually adhered to, will deliver the desired play experience.
People making up a game and trying out rules on the fly aren't playing a game.
This isn't actually true, as [MENTION=22779]Hussar[/MENTION] points out. I have two young children, and they play games all the time in which rules are made up on the fly - mostly variants of "let's pretend".
There are modern RPGs which don't require rules to be made up on the fly (eg HeroWars/Quest), but the only version of D&D that comes close to this is 4e.
Most kids, at least in the Milwaukee area in the early to mid-1980s, knew the DM wasn't supposed to make things up behind the screen. That's why all the rules were there.
All of these games, including D&D, are predicated on the act of game play, that players are deciphering an underlying code to attain objectives in a pattern, i.e. a game.
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To Hit, damage, and Hit Point stats are obviously all over D&D. That they are based on underlying patterns so items like hammers and pitons and portcullis mechanism (a winch or chain pulley?) can also be derived from the same is less obvious. But many wargames did exactly that. They derived results from the game's design.
This doesn't actual adjudicate anything. You have not stated any rule. (What you say is also not true. Very few non-creatures in AD&D have AC and hit points - the Rope of Entanglement comes to mind, and there are probably others. The siege rules, though, which are the biggest chunck of rules in AD&D for dealing damage to non-combat things, and it uses different to hit rules (all targets are deemed either AC 0 or AC 10, depending on attack mode) and a different damage system.)
I'll repeat my question. The PCs are in a dungeon corridor. Between them and the onrushing orcs is a portcullis, currently raised. The players form the view that there is no time to lower the portcullis in the conventional manner, but one of them decides to use a hammer and piton to break the mechanism and thereby have the portcullis drop into position, blocking the orcs. How is this to be resolved?
You have suggested it should be resolved using the combat mechanics. That is not obvious, though (for instance, opening doors and bending bars/lifting gates have their own, level-independent, stat-based method of resolution). But let's play along. What is the AC of a winch mechanism? How many hit points does it have? And how much damage does a hammer and piton do?
In order to resolve the situation I have described the GM has to make all that stuff up, either when writing up the dungeon description if s/he thinks of it, but - more likely - when the player declares the action.
From the point of view of play, it makes no difference when the GM makes it up (unless you a very worried about the GM being biased by the actual fact of action declaration). In this respect, the mechanics for shattering a winch mechanicsm are not very analogous to the number of orcs in room 10. The latter shoud be a secret from the players until their somehow perceive (via sight, ESP etc) the number of orcs in the room. But the former can be known to the players any time they ask "What are the mechanics for shattering a winch with a hammer and piton?"
The DMG is advice to DMs to build their game prior to play
This simply isn't true - the DMG includes both advice on how to build a dungeon, campaign world etc prior to play, and also contains advice on action resolution.
Here is one example of its advice on action resolution (p 97):
You may use either of two methods to allow discovery of the mechanicsm which operates [a secret door]:
1. You may designate probability by a linear curve, typically with a d6. Thus, a secret door is discovered 1 in 6 . . .
2. You may have the discovery of the existence of the secret door enable player characters to attempt to operate it by actual manipulation, i.e. the players concerned give instructions as to how they will have their characters attempt to make it functin: "Turn te wall sconce.", "Slide it left.", "Press the samll protrusion, and see if it pivots.", "Pull the chain."
It is quite acceptable to have a mixture of methods of discovering the operation of [a] secret door.
Here is another, which I mentioned upthread, on secondary skills (p 12):
When secondary skills are used, it s up to the DM to create and/or adjudicate situations in which these skills are used or useful to the player character. As a general rules, having a skill will give the character the ability to determine the general worth and soundness of an item, the ability to find food, make small repairs, or actualy construct (crude) items. . . . To determine the extent of knowledge in question, simply assume the role of one of these skills, one that you know a little something about, and dtermine what could be done with this knowledge. Use this as a scale to weigh the relative ability of characters with secondary skils.
This is advice to a GM on how to improvise adjudications of players' use of their PCs secondary skills. Right there on page 12 of Gygax's DMG.
in AD&D, how you do adjudicate someone jumping over a pit. You could do a Str Check, you could do a Dex Check, you could rule by fiat, you could choose a Saving Throw, and i'm sure there are other ways.
If the rules were set before play started, how would you perform actions that aren't listed in the game?
I have asked this question many times over the months and years, but have never recieved an answer.
It is particularly odd in the context of someone emphasising D&D "as it was meant to be played", given that off-the-wall actions based around manipulating the imagined environment of the dungeon were a bigger part of classic D&D play than they are of most contemporary games. It doesn't get any more old-school than surfing doors that have been removed from their hinges over super-tetanus pits in the frictionless corridor in White Plume Mountain, but the game has no mechanics to resolve that (either the door removal or the surfing). It's all up to GM adjudication!
Funny how history works.
