I think that kind of demonstrates Gaiman's principle, doesn't it? Regardless of the power and logical capabilities of the adversary, the human beats them, because that's the point of the story.
It depends on the story, and the audience.
Going to the OP, the Gaiman quote
in Coraline in the epigraph (not
why he wrote Coraline) is:
"Fairy tales are more than true: not because they tell us that dragons exist, but because they tell us that dragons can be beaten."
This is a paraphrase of the G.K. Chesterton quote:
"The timidity of the child or the savage is entirely reasonable; they are alarmed at this world, because this world is a very alarming place. They dislike being alone because it is verily and indeed an awful idea to be alone. Barbarians fear the unknown for the same reason that Agnostics worship it—because it is a fact. Fairy tales, then, are not responsible for producing in children fear, or any of the shapes of fear; fairy tales do not give the child the idea of the evil or the ugly; that is in the child already, because it is in the world already.
Fairy tales do not give the child his first idea of bogey. What fairy tales give the child is his first clear idea of the possible defeat of bogey. The baby has known the dragon intimately ever since he had an imagination. What the fairy tale provides for him is a St. George to kill the dragon.
Exactly what the fairy tale does is this: it accustoms him for a series of clear pictures to the idea that these limitless terrors had a limit, that these shapeless enemies have enemies in the knights of God, that there is something in the universe more mystical than darkness, and stronger than strong fear."
Setting aside the clear ... let us say
point of view that G.K. Chesterton is known for, the thrust of the quote is clear; a fairy tale has an audience (little kids) and a message (that fear, no matter how awful, can and will be overcome). Whether you view this as banal or brilliant depends on you, I suppose. I might also say that this formulation very much depends on the later, more sanitized fairy tales that were circulating by the time Chesterton was writing, but that's a separate issue.
None of this is particularly relevant, in my opinion, to either different types of fiction or, necessarily, to games such as D&D. For example, I doubt very much that H.P. Lovecraft was sitting down at his desk and thinking, "Well, other than including some racism, I need to make absolutely sure that my protagonists can defeat Cthulhu, because I wouldn't want to give the reader the wrong idea!" For that matter, I am fairly certain that Ian McEwan wasn't thinking, while writing
Atonement, "Yeah, actions might have consequences, but I have to aim for that happy ending!"
It's the same with any given RPG; perhaps you are playing something where everything is measured in hit points, and monsters are just big bags of XP to help PCs level up and provide magic items. Maybe any given critter can be defeated- but the PCs would need the appropriate power (level) and preparation and, perhaps, a little luck in the form of die rolls. Or maybe there will be scenarios where "winning" is simply choosing the best losing scenario.
Saying that any given RPG has to function a certain way is the same as saying that all literature would have to function by Chesteron's instructions for fairy tales; I think the world would be a much poorer place. There is room enough for a plethora of different types of play, and I would hate to see it hamstrung by attempts to so limit it.