I agree that you're challenging the players. That is why in my first post in this thread I identified this sort of thing as one of the ways in which a game can challenge the players, and in my later post I identified "fact introduction" as how I would use Diplomacy in the Moria gate encounter.I guess what I'm not following is, in my example, why do you say the players aren't challenged? (" ..disliked by those who favour the 'challenge the players' approach")
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Is it because the players made their own success instead of figuring out what the DM wants them to do? While there is a time and place for puzzles that are basically 'guess what the DM is thinking,' too many can become very railroad very fast, IMHO.
But by "challenge the players" approach I meant those who agree with the OP. As far as I can tell, by "challenging the players" they mean not the sort of thing you talk about, but rather a module like White Plume Mountain or The Tomb of Horrors, where (i) there is no overt metagame (whereas in your example of the players getting to make stuff up abouot the gameworld there is a various obvious metagame, as what the players are doing in no way corresponds to what their PCs are doing), and (ii) there are no action resolution mechanics like skill checks (a la Runequest, Rolemaster, Wilderness Survival Guide, 3E etc) or skill challenges (a la 4e, HeroWars/Quest, The Dying Earth etc) - rather, the player describes what his/her PC is doing and the GM adjudicates it.
I agree with you that the sort of play I've just described can become very railroad very fast if the players and GM are not on the same page.
But equally, I have to acknowledge that a lot of posters on this forum don't seem to like the metagamey sort of play which allows players to make skill checks for fact introduction. They only want the skill check to reflect the PC actually doing something in the gameworld (or else, as with the OP, they don't want skill checks at all). And a recent thread on Saying Yes had a lot of outrage about the passage on p 28 of the 4e DMG, which involves a player engaging in fact introduction" with respect to the challenge suffered by, and reward received by, his PC (so slightly more extensive fact introduction than the sort you talked about).
The best actual-play examples of fact introduction in the context of 4e that I've seen on these boards are posted by Lost Soul. A recent one, which involves a skill check just like in your example, is here. But I think what he is describing here is exactly the sort of thing a lot of people seem not to like about 4e.