Well, to borrow from Ron Edwards, there are three basic ways to resolve action declarations in a RPG:I haven't played Dungeon World, but this is disheartening. I was understanding it as a game that steps away from dice instead of one stepping toward them.
* Drama: someone narrates what happens;
* Karma: a number/rating determines the outcome;
* Fortune: dice, cards etc determine what happens.
* Karma: a number/rating determines the outcome;
* Fortune: dice, cards etc determine what happens.
Drama resolution has its place (eg it's the "yes" in "say 'yes' or roll the dice"), but I don't think a game where it covers the field will be very satisfactory. Going back to the pile of rubble: if the player is allowed to just narrate what his/her PC finds, that seems a bit easy (and potentially quite insipid) unless it's pretty low stakes, in which case it's not the main action in any event; and if the GM just narrates what the PC finds, then we've got strongly GM-driven play, which can be fine in modest doses but certainly isn't the main thing I'm looking for in RPGing. And it's certainly not what Dungeon World is about!
So it's either karma or fortune - and DW goes with fortune. A strong success (10+) gives win. A modest success (7-9) gives small win, or win with cost. A failure (6 or down) gives 1 XP, and licenses the GM to make a move that is adverse to the interests of the PC in question.
I haven't played much DW, but am hoping to get a bit more experience with it maybe over the next year or so (maybe when my group finishes our Cortex+ Heroic Fantasy game, I'll be able to persaude them to try DW in its place). Both from experience and by reputation, it seems to play pretty well.