Obviously people can be wrong, but so can complex game mechanics.
Yes, but at least the game mechanics will be presenting the
same assumptions to everybody. Once its personal perception, you're living inside someone's mind, probably the GM's, and not everyone is going to think to ask the GM all the time (and that by itself is an opportunity cost).
When would you prefer a gamemaster’s judgment call, and when would you prefer a canonical ruling tucked away in a rules supplement somewhere with a mechanic that may or may not yield more accurate results?
I'm less concerned about accuracy than consistently, and you're cooking the books by assuming its only a suppiment and not easily accessible. If that's your overland speed, that's just another indication of bad rules design. It should be a core rules things and fairly visible.
Basically, the only time I think a GM judgement should be entirely necessary in something like this is what I mentioned earlier--situations outside the normal scope of the game. They're going to have to decide how the extent rules are engaged (how steep is that cliff you're climbing) but they shouldn't be needing to make them up out of whole cloth.
For something that exists in the real world that we expect to come up regularly in the game, we’d want someone to do the research and summarize the results with, for example, a list of typical marching rates over various kinds of terrain. That’s the kind of real-world information you’d expect a wargame umpire to use in a map-based simulation.
Actually, its what I'd expect their rules set to have already done for them.
In a hex-based wargame, you’d simply move your allowable number of spaces, with rough terrain costing double, etc., and there’d be zero room for improvising, because nothing outside the explicit rules is even an option.
And?
Almost everything that happens in an RPG is outside the scope of the rules, and that works fine. Other things don’t need rules per se, but they have a right answer you;d like to be able to look up easily. How much does a warhorse weigh? How thick is a guard tower wall? Some things benefit greatly from rules, but not everything.
i disagree. Most things are well within the scope of properly designed rules. They may vary from the common case, but they won't be entirely new situations that have no rules precedent. If they do, you're working with overly lightweight or sloppy rules as far as I'm concerned.