AbdulAlhazred
Legend
Well, I agree that it will have to be bound by existing fiction, genre expectations, and such. Presumably if the answer is 'out there' in terms of not seemingly plausible (Orcs can go without food for 10 years) then this will have to be worked into the fiction, and should PROBABLY already have been established.It doesn't have to be "purely gamist reasons". Sure, the DM isn't going to have that level of detail and will need to make something up, but that doesn't mean the DM can't try to make a reasonable extrapolation from established facts in the game world. Sure, there will be inevitably be some gamist component to the decision (and I don't consider that a bad thing), but the decision doesn't need to be exclusively gamist.
I just mean, its hard to really judge something like "is there enough water supply in the orc lair?" Any answer will be significant in a siege situation where it is coming up. I don't know what criteria you would use to decide, given that the GM's answer is unconstrained by existing fiction.