Thanks for engaging substantively, Manbearcat. I want to make sure I know where you're coming from on the idea of new rule-like things that still don't count as rules. Since I'm not familiar with Dungeon World terminology, could we examine the same situation (opening a sewer hatch) from the perspective of AD&D to see if these also don't count as rules in your eyes, or if there's something special and different about Dungeon World?
Player wants to open the sewer hatch. DM specifies Open Doors roll at -2 to pull open. Player fails. Ties a rope to the sewer hatch, sets up a pulley system as a force multiplier. DM allows this to give a +6 bonus on the Open Door roll but says that if it fails then that means the rope snapped. Player succeeds and DM gives them a 50% chance of being drenched in sewer water spraying out of the hatch (they roll 2 on a d6 and do get drenched) but this turns out to be a valid back door into the area where the princess is being held hostage.
Same scenario as the Dungeon World custom move for sewer hatches quoted above. Same degree of reasonable extrapolation to cover scenarios not spelled out explicitly AFAIK in the AD&D rulebooks (pulleys and rope strength; probability of getting drenched by a nearby liquid steam).
This ruling works within the unifying structure of the game (success rolls against a value on a table, in this case Str table for a feat of strength). I don't grok the meaning behind your words like "unifying agenda" and "give expression to some aspect of the game rather than subvert it", but I don't think you're saying anything that would make using ropes and pulleys a form of subverting the game. It seems to me that all the things you're saying about Dungeon World apply equally to this AD&D scenario.
Would you say that this scenario also doesn't rise to the level of new AD&D ad hoc rule creation? In my mind when I talk about the need for a GM to improvise rulings and rules to cover gaps, this type of thing (extrapolating how much pulleys multiply your effectiveness) is indeed included, but do you disagree?
Well, the two scenarios differ in one fairly important point. The DW custom move does NOT have anything to do with determining if the hatch opens or not. It is a way of letting the player choose between various options WHEN a hatch is opened. So, the player rolls after saying "I open the sewer hatch", triggering the move. The player then has to decide, do I find a way to my goal (the merchant's daughter) OR do I avoid nasty filth and/or a gelatinous cube? Remember, getting to these hatches may be, in and of itself, a chore which exposes the characters to some danger (we don't know, but its possible). So, lets say I roll a 7, now, I can, at the cost of getting covered in filth and eaten by a GC find the way to my goal. OR I can avoid one of the other consequences, not get the daughter, and go on to a different hatch later, where I will hope to roll a 10+.
I think this is much different from the situation with the AD&D version, which is basically all about task resolution, could leave us with no way through the hatch (I guess we can now go on and invent more rulings related to whatever spell, etc. we try next). There's no question here of a trade off, nothing, its all straight up linear 'open the door or fail'.
However, I don't think any of that really answers the question of what is a rule vs what is a use of the existing rules. In the AD&D case no actual rule was created, there was an adjudication that using a rope and pulley gave a certain bonus on a roll, etc. I kinda feel like this is incomplete rules in that AD&D doesn't really tell us when to use 'open doors' vs 'BBLG' and such things. I mean, I'm OK with someone saying it is just 'using the rules', but the DW case seems FAR less that way.
To see why, read the rest of page 347! It talks about how this entire thing COULD be handled using Defy Danger. DD is a perfectly reasonable approach, it just doesn't neatly capture the trade offs that the players need to make when they open a hatch. Clearly the GM could say "Oh, you got a 10+ on DD, nothing hurts you" but we won't get the whole "and is the princess here or not" part. Either the GM will have to designate on his map a specific hatch where the Princess is, or some additional narrative will be needed to figure that out. I just see the 'Open the Hatch' move as a way of condensing that. Its more environmental design and adventure design than it is some kind of rule.
So, reasonably, the AD&D one is NOT making a rule, as if it is then pretty much everything the GM says in AD&D is making a rule! Likewise, I don't think its making a rule in DW either, as otherwise every time a GM maps out a dungeon they're 'writing rules' and that surely seems wrong to me.