That's the problem with Gizmo's quote. He's pulled it completely out of context and ignored everything that comes before and after. For two pages before the quote, the DMG spends a great deal of time making sure that a new DM will absolutely be forthcoming with information that is necessary, and gives a number of techniques with which to pass information along to the players. The next couple of pages talk about what happens and what to do when the players do take a sharp left turn.
No "context" does not mean that I can give a speech standing next to a dictionary and every time I say something foolish I can then pull out the dictionary and then claim that there was other stuff I was about to say that invalidated it. That's becoming a very old trick. The author establishes the conditions, and then suggests the solution. The proximity of these other statements is irrelevant. That information is never referenced. It's not part of the context of the statement.
I've already been clear about what the DMG is trying to say in that section, and it has nothing to do with these other sections your talking about. HAD Wyatt (assuming he authored all of this) actually taken seriously his advice on improvising, delegating, the different player motivations, paying attention, and so on then it would have RENDERED MEANINGLESS the statement about "short circuiting" the "whole adventure." How is it possible to "render a whole adventure meaningless" given that the definition of a successful campaign includes this myriad of elements. And many of those elements are player dependant - but this isn't recognized, seemingly, by many of the advocates of the "lie to the player" approach. You scratch the surface IMO, and find that the DM has been this secret Prima Donna this whole time, and the con that he gets the players to get involved in his story is based on an illusion (not well maintained) that they are playing a game. For example:
page 33: "The Core Mechanic: Explain the core mechanic of the game: Make a check and compare it to a defense."
No - that's not the core mechanic apparently. The core mechanic in the game is that stuff happens when it suits the DMs plot. You only roll dice when the outcome doesn't change this fundemental framework established by the DM.
A plot, AFAICT is just a series of the most interesting and important events in a story. If you have an attitude, as a DM, that the plot is 100% within your control, then it seems to me that what you're really saying is that the players - through their decisions, luck, or whatever, have no control over any of the real interesting parts of the game. They can control whether or not they kill the monsters in 4 or 7 rounds, I suppose.