Oh, I agree Mike. But Damage isn't strict either. I see it as a 'Guide' to the monster's potential. I mean, if you want, you could just kill 'em all with an earthquake too, but that would be a dick move.
When Fizbo the wizard misses his hack and slash with the giant, I could make my monster move and say hurl the wizard against a cavern wall... But I also decide to deal damage (as warranted by the fiction). Now that could be the Giant's damage that it deals as listed in its stat block. Or I could ask the fighter 'Hey Groo, you've fought giants before right? Is that sickening crunch as Fizbo hits the stalagmites got you worried?' You know that the giant's damage as listed will kill the wizard, and you are a fan of the character's right?
You could knock Fizbo out, forgetting all his spells.
You could break his bones, or cripple him permanently.
You could bounce him painfully off the stalagmites and have him clinging precariously to the edge of a subterranean abyss. Groo can either save him from certain death or attack the Giant, what does he do?
You could have his bundle of books save his scrwany hide but get pierced by the stalagmites and use up his resources.
You could impale his leg on a needle thin stagalmite causing the loss of all his HP bar one and have (up until this point) the trustworthy goblin guide named Snitch smirk evilly as he draws a rusty dagger and approaches Fizbo to 'help'.
You could disclaim decision making, ask questions and use what they give you, thus letting Groo's answer guide the fiction (or if he waxes lyrical - snowball and say, 'hmmmm sounds like you are spouting lore...').
Or you could just deal the Giant's damage and have Fizbo make the death move.
They are all vaild moves, I personally feel that the fictional ramifications have far more tension ridden 'weight' that simply choosing to either deal damage as established (or roll monster damage if that's your thing). And simply rolling the death move. The more I can tie the immediate fiction into the mechanics, the more weight our story has.
I really like telling them the consequences and asking. Foreshadow the pain and suffering. You know that the Giants stat block lists its damage as enough to kill all the PC's with one or two blows. Show them that doom! Have the Giant smash shit in front of them, crushing dwarven architecture into splinters. If they really decide that attacking the Giant is worth the risk, despite the fact you've said 'Hey, y'know one blow from his meaty fist will crush your bones into jelly', then by all means deal 500 damage.
I think the most powerful part of the game is the emergent potential of monsters as they are seated within your dungeon world, as tools of the story. Monsters exist to illustrate what a dangerous awful place Dungeon World can be, so illustrate with their moves, and deal damage as appropriate.