Enough of the trip down memory lane, the point remains I started with an RPG that was a game, first and foremost. The whole G in RPG. We must have played D&D literally every day for 6 months, the weekends spent on sessions spanning multiple days. From 8th grade until around 10th, I played constantly, and it was almost an obsession. Shortly thereafter, I got burned out and began playing sports, but still found time every so often to revisit a quick game with friends. But, it was always a game. There was no "performance art" crap going on, no "character development", and certainly nothing what could be called, in the more modern sense, "role playing". We were simply a bunch of kids playing a game, and only a game, wherein our characters were no more identified with us than knights or rooks during a game of chess. Character death was Bad, not because we had labored so long to create a persona with an intricate background, but because we'd have to roll up a new character and start over. Sometimes we'd roll up a character with a lot of money. One of the other players might then murder this character and steal the money to purchase new armor. Roll up another character!
I bring all this up as a backdrop to the real reason for this post, namely that D&D has a lot of built-in assumptions due to it being merely a game. The primary, I think, is the idea of a "mythic underworld" existing, just outside of human civilization. Many others have explored this idea in great detail, and by no means do I want to infringe on their work, but I think it's a valuable notion that can be discussed further.
Take a look at the box/manual artwork for Wizard's Crown, a game I played relentlessly for years. Regrettably, I never did complete it, but it surely wasn't for lack of effort. Anyway, doesn't THIS evoke exactly what D&D is all about? A band of adventurers fighting foes through the ruins of a prior, more advanced civilization, culminating with a showdown inside a grandiose castle, inhabited by a nefarious wizard. I think Swords & Sorcery, and by extension D&D, must operate with the assumption that in the past, there was a great empire expanding countless continents, etc., which suddenly fell. Years later a different form of civilization cropped up, with no knowledge of the former except as legends, seeking out treasures in the ruins of old.
In my mind, the "D&D world" is large, perhaps as large as Earth, maybe bigger, yet extremely encapsulated. By this I mean that small villages exist all over the place, but people rarely, if ever, travel outside of theirs. The world is almost in a constant state of gloom, and just outside of town there are hills dotted with trees, perpetually in autumn colors. Crevasses and pits are visible in the rolling landscape, with shining eyes peeking out when the sun goes down. Children don't stay out after dark, for fear of being taken by goblins, put to work in their mines. Dwarves and elves are mentioned ever so rarely, as humanity has almost lost all contact with them, and their presence brings many stares of disbelief. There is an old tower looming across the landscape, some say a necromancer still resides within its walls, others insist it has been taken over by the animated remains of armies long past. There are a few who can use the healing touch, but they are mostly shunned unless needed. And dragons? Yearly sacrifices are made to keep the monster at bay, perhaps a choice village virgin. What lies beyond the furthest hills no one can say, as travelers from distant lands cannot be trusted.
That's my idea of a "D&D world", the almost static, yet still decaying, state into which a previously wondrous world has fallen, ripe with opportunity for those who would simply take it. Dangerous only outside the confines of town, but filled with death at every turn once those confines are left. It's the same world that Grimm's Fairy Tales take place, a locale that can be left and come back to on a moment's notice without feeling anything was missed. And that's why it is a GAME WORLD, because its purpose is to allow for meaningful gameplay within the confines of a rules-set. I am unconcerned with monster ecology, how ogres sit in a 10'x10' room, waiting to waylay unwary delvers, but serving no real purpose otherwise. We can roll dice all day long, and "fight ogres", but only when we go meet them on their turf, in the underworld that persists just outside human influence, does it become more than an exercise in die rolling and become a game, something fun.
Surely others will disagree with me here, and plenty of people want something else from their D&D games (I say this instead of more simply because what reason is there for playing other than to have fun?). However, I think that treating the game itself as nothing more than a game leads one to realize the underpinnings are not only less interesting, but lead to possibly much more entertaining endeavors. After all, what are RPGs about besides killing orcs and taking their loot?