I'm honestly not sure what people mean when they say 'play to find out what happens', I've seen it used in a load of different ways. Same with Sandbox really, two people can say they run a sandbox but recoil in horror when they learn what the other one means.
To use a previous example. If three characters go and fight six characters at the abandoned water works, then both GURPS and Apocalypse World give us a method of finding out what happens.
It's only the introduction of tech like fudging the dice or suddenly deciding other people show up out of nowhere, that changes 'find out what happens' to the GM forcing the issue.
Ok, so
none of what you described is "play to find out what happens"
What it means is "
The GM ALSO has no idea what will occur next in ANYTHING - especially the plot and scenes and events." This goes back to my earlier posts about Modern Mechanics are limiting the GM, rules to tell the GM "No, the players runs this part, and you get no ruling in it".
What PBTA does is what GURPS could never do, by design - let the engine make the events and plots for you.
Examples:
- In Monster Hearts you can roll to interact with someone, and even attack them - only for
the rules to tell you that your character is now infatuated or aroused by the enemy, and you are expected to run with that.
- In Passion de las Pasiones, a move allows a player to state that someone is lying (anyone, PC, NPC, etc) about anything, even plots and events in front of them, and they can state the 'actual truth'.
If they make their roll, they are right and everyone else was lying (wrong). So plots must adjust and go from this new truth.
- In Apocalypse World there are several moves that add to the fiction,
the rules state that this NPC will now betray you, and its only up to the MC as to where and when. Sure they may be an ally or a lover, but they will betray you!
- In most any PBTA game, the moves describe what happens as a result of your drama. They are interpreted by the players, but
they can add all kinds of things to a game - including enemies that were not there before, locations that were never placed by the GM, and even plots that take on a life of their own as a myriad of Moves alter and change and update the truths of the plot - even unto retconning previous truths!
GURPS is "task resolution". The GM presents things to do, has some idea of the threats or risks involved, and when you roll, it only tells you one thing = you did the task or you failed the task.
That's it, full stop. The Gm may choose what happens next, but the roll didn't tell them what to do, only that the player did or didn't do the task that was already in front of them.
Nothing was found out or discovered, it was just "resolved".
PBTA is a "Drama engine". The game moves introduce new features in the game, and add plots when there were none. PBTA has no skills, and considers nothing a 'task'. You are making dice roll in terms of 'overall goal' or 'interacting with a plot.' There is nothing to pass or fail. Instead it is all about "
and here is extra stuff to create the story and where it goes next."