I think there's a difference here. Mort suggests (and plenty of others believe) a player should have his or her character act a particular way, when that is not backed by the rules of the game we're playing and is easily explained given the mutability of the fiction. Whereas the rules saying the DM should be judging the efficacy of a player's stated approach to the goal is telling the person choosing to be DM about his or her role in the game.I think there is at least a modest tension between these two posts - which are from different posters, but posters who generally seem to be in agreement on most of the issues under discussion on these threads.
A GM judging whether an approach is a clever and/or logical one seems to be imposing shoulds - and relying on robust counterfactual assumptions more generally.
I think it makes sense to talk about who has authority over what aspects of the fiction; but I don't think it helps to explain this in terms of the robustness of "should" in a game of imagination.