William Gibson wrote in his book Pattern Recognition about the concept of a Mirror World. The Wikipedia masses define the newly-coined term “to acknowledge a locational-specific distinction in a manufactured object that emerged from a parallel development process, for example opposite-side driving or varied electrical outlets.” I think the excellent term does not need to be so constrained, and it may be as broad as “fundamentally the same, but elementally different.” This happens for better or worse all the time with MMOs. Take, for instance, the way an MMO tells its story:
In Warhammer Online the main story for each race is broken up between normal quests, epic quests (spanning across Chapters, differentiated only by an icon), and the Tome of Knowledge. If an avid (or obsessive) gamer reads across the three storytelling mechanics a very comprehensive, detailed story emerges. The problem is that most of the shiny story bits are lost in a lot of muck. In other words there are a lot of quests and Tome of Knowledge fluff that have nothing to do with the overall story.
Lord of the Rings Online deemphasizes the Tome of Knowledge-type mechanic (though there are plenty of small story bits if you scroll over the Deeds) and parses out the main story to turn epic quests in to Epic Quests. Lord of the Rings Online also uses instancing for the more crucial parts of its story, and recently it started using camera-style cinematics for when Aragon needs to talk to you.
Guild Wars has no Tome of Knowledge analogue, but most of its story is well-told in the form of Missions with quests filling in the gaps. It has used the camera-style cinematics from the game’s inception, and beating the Campaign is at the front end of gameplay. The game is furthermore content-gated based on which Missions the player has beaten so players going the PvE route have little choice but to experience the story.
Each game is fundamentally the same in that a story is told as the player progresses through the levels and zones. In Warhammer Online, I would guess that very few players are aware of the, in my humble opinion, pretty good story as they go from one red blob on the map to another. In Lord of the Rings, where many Tolkien-priests reside, players are well aware of the story, but many skip much of the epic quests in order to go fight a Balrog in the dungeons. Finally, in Guild Wars, for better or worse, everybody goes through the story.