I don't think you're off base, and it's a pretty common feeling among a lot of gamers--your position of "it's a fantasy game with magic and monsters, so why question realism at all?" But on the other side, it's been sort of an unspoken rule that anything not explicitly called out with why/how it breaks realism would be based on realism. We all need that baseline of expectations that is founded on our real world experiences. Otherwise that logic is a slippery slope.
For example, where does it end?
"Well, my fighter can suddenly cast magic despite nothing he or she has done in the adventure so far that had anything remotely to do with magic because it's a fantasy game with magic and monsters!"
"Oh, my character doesn't drown, because he or she doesn't need air to breath, because it's a fantasy game with magic and monsters!"
"I don't take any damage from that falling boulder because physics doesn't work like that, because it's a fantasy game with magic and monsters!"
Every table bases everything going on in the game world around realism unless there is something specific that overrides it, from climate, to eating and sleeping, to gravity, to how rivers run, to biology, etc etc. It really comes down to a personal preference on where that line is drawn. So making a blanket statement that things shouldn't be questioned "..because it's a fantasy game with magic and monsters!" isn't the best argument, IMO, because that's how you might feel, and not other players. Subjective vs. objective.
