When people have an instinctive "it feels like we should be rolling dice here, which move should we use?" reaction I think it's just fine for the answer to be "actually, we don't roll dice for that in this game".

Yes! … but my summary had to end somewhere.
Catch-All Move is very much meant in a "There is no move, but there definitely is a risk (as per the fictional requirement of Act under fire e.g.)-Move" way. To do it, do it, don't roll dice to walk to the other side of the room, or to see if you spot something by pure chance – which is somewhat what I meant with "Please roll a dice, because reasons" does not work in PbtA.

To my mind, "catch-all" style thinking is closer an "I'll just say stuff and let somebody else think about the mechanics" style of play.

Which is one of the core things in practice of PbtA:
Saying what you want to do, and asking the GM whether what you think you should roll actually applies.
As you said, in PbtA GMs should not be afraid of saying things like: "This NPC has no chance of defending, you just deal your damage, and kill them; no roll required".

an NPC had a gun to a PC's head, the PC tried some psychic manipulation and got a 6- roll, the GM tried to have the NPC get all flustered and just graze the PC with a gunshot, but the player felt that was really cheesy, that their character dying was the only reasonable resolution to the interaction.

Which definitely is a case, imo, where death fits the fiction well. As you mentioned: Say what honesty demands, but also letting everything flow from the fiction and making the world seem real.

The "death fitting the story" thing was obviously meant as a "jab" at DnD in regards to my recent blog-entry about fudging dice rolls. 3 goblins against a Level 4 DnD party should not be a threat, story-wise, but if the dice think that goblins should only roll 18+ and players only 3- for an hour …
Death was basically out of the question, but DnD is no story game. In DnD the players might die horribly, while in Dungeon World … The players might also die if the dice really tell a "the PCs die to measly goblins now" story (and we're here to play to find out what happens, if this is what happens: okay?!), but the GM has way more ways to spin it towards not death, than in DnD.
Not that the GM should bend reality for it – In Dungeon World you can still do a
"The Dragon is about to kill you, and then … he flies off, because reasons!"
"Ah, okay, the GM doesn't want to kill us, everyone ¬_¬"
just like in DnD, of course.

But if the character is proactive they're probably going to be making a lot of player-faced moves, which are often successful at getting them what they're going after.

This is a very good way of phrasing what I wanted to say, but failed at, with my "Players will eventually reach their goals, and are thus encouraged to pursue them." – even their active pursuit is being rewarded.