Ok, going back to the actual topic..
Orion wrote:"Don't prep plots" and "play to find out what happens" just mean that it's improvistaional single-author storytelling rather than scripted single-author storytelling. They don't guarantee that the players contribute anything.
Except the book explicitly contradicts you:
Pg 108, Apocalypse World wrote:
"Play to find out what happens: there’s a certain discipline you need in order to MC Apocalypse World. You have to commit yourself to thegame’s fiction’s own internal logic and causality, driven by the players’ characters. You have to open yourself to caring what happens, but when it comes time to say what happens, you have to set what you hope for aside. The reward for MCing, for this kind of GMing, comes with the discipline. When you find something you genuinely care about — a question about what will happen that you genuinely want to find out — letting the game’s fiction decide it is uniquely satisfying."
See that "driven by the players characters" over there ?
Besides it, there are various other passages in the GM chapter where the author explicitly instructs about the importance of following though the players inputs. See: (I emphasized important parts, if you dont want to read the whole thing)
Apocalypse World wrote:"Ask provocative questions and build on the answers. Start simple: “What’s your living space like?” “Who’s known each other longest?” But as play proceeds, ask for immediate and intimate details of the characters’ experiences.... Once you have the player’s answer, build on it.... refer to it later in play, bringing it back into currency; and use it to inform your own developing apocalyptic aesthetic, incorporating it — and more importantly, its implications — into your own vision."
"Always give the characters what they work for! the way to make a character’s success interesting is to make it consequential. When a character accomplishes something, have all of your NPCs respond. Reevaluate all those PC–NPC–PC triangles you’ve been creating. Whose needs
change? Whose opinions change? Who was an enemy, but now is afraid; who was an enemy, but now sees better opportunities as an ally? Let the characters’ successes make waves outward, let them topple the already unstable situation. There are no status quos in Apocalypse World! Even life doesn’t always suck. "
"Springboard off character creation: The players’ characters are made of interesting details you can build on. Look at the hardholder’s gigs, for instance: each of those gigs has people responsible for it, crews that answer to the hardholder and have names and relationships and all kinds of loose ends. Name everyone! Make everyone human! Look at the Chopper’s gang,
the operator’s crew, the hocus’ followers. Look at what the players created when they were doing Hx with each other. Look at where they come from and what must be around them."
"Ask questions like crazy. Ask about the landscape, the sky, the people and their broken lives too, don’t just tell, share. Turn a player’s question over to the group: “I don’t know, where DO you get your food?” But especially, anything you want to know, ask. Anything you think might be interesting later, ask. Anything a player says that sticks out, anything that seems like the tip of an iceberg, or like fish moving under water, ask."
"Nudge the players to have their characters make moves. Start with the characters with beginning-of-session moves: the hardholder, the operator, the hocus, the savvyhead, if you’ve got them. That’s now, the first beginning of the first session. Have them make those moves and follow what happens. Then throughout the session, remind everyone to look at their character sheets to see what moves they might make."
"Build on what the players said when they introduced their characters. “So Keeler, Marie, you two have this raiding thing out on the wilderness road, where Marie stands lookout and Keeler attacks travelers in the night? Let’s see that. It’s before dawn…”
Aside from play instructions by the author, there are 2 other elements that
enforce the player-driven nature of the game:
1) The First Session sheet. This is the game "mission control", where the GM tracks all entities the group is dealing with in a way or another. And this is explicitly built
through the input of the player-characters - threats, friendlies, suppliers, buyers, holdings, cults, you name it, all come from the players inputs in the first session, and from there it sets the direction the whole campaign will follow.
2) Player "moves". The ones from enterpreneur playbooks (Hardholder, Operator, Hocus, etc) are specially disruptive for the current "game-state" (since they can obligate the GM to produce entire entites or events from scratch, depending on what the player chooses for their starting stuff, or how good or bad the player rolls on specific situatoins), but even simple ones like "Lost" from the Skinner (which makes you call a person by name while on a dream and then he/she simply comes for you whatever the situation) can exert a considerable force on the game's direction. Even
Read a sitch and
Act under Fire - basic moves that all characters share - exerts a strong direction on the game, as it may oblige the GM to establish pieces of fiction (and follow through with them), even if it wasnt considered before.
Notice that yes, the GM will be improvising a lot of things out there, but he only does so
at the players prompts. Moves are game-state changers, and thus, dictate the game directions. The GM will also have input in the process as, sometimes, the specifics of the fiction will be created from scratch, but even then, he is obligued to create things that are coherent with the situation at hand,
and with the players intentions in the first place.