Majoru Oakheart
Adventurer
As a side bar, I would get to this point like you did but my next line would differ slightly...
Me: "This one's not afraid of water how odd...what's your AC again?
Our group would just never stand for a DM doing something like that. We always had a rather adversarial relationship with our DM, however.
I can see how this conversation would go:
Player: "It's not afraid of water? But they were created with a fear of water by the great wizard, Falstaff when he created their race 2000 years ago. ALL of them are afraid of water. They explained that in Book 3 of the Falstaff Trilogy. An archmage attempted to use magic in that book to remove their fear of water and found out it was impossible.
I find it EXTREMELY unlikely that this one managed to find an Epic level Wizard with the power to remove this limitation considering the only Epic level Wizards on the planet are Elminster, Blackstaff, Joe the Plumber, and Megatron. Elminster is currently battling his way out of hell as per the book Elminister versus the Devil, Blackstaff is evil and hates Minotaurs, Joe the Plumber is currently in a deep sleep for the next 100 years, and Megatron cares too much about Energon to spend time curing Minotaurs.
Look, it's obvious that you are just making things up rather than running this campaign setting properly. You had no idea that that type of Minotaur was afraid of water. That's fine. I'm sure he's really an Orc or something rather than a Minotaur. But next time you should really read the books before running a game set in this campaign world."
DM: "Umm...yeah, he's an Orc."
But our group always worked on the assumption that anything published in a book was LAW. Game books or novels alike. If the DM made a mistake and you pointed out the correct answer, the DM was obligated to follow the "correct" source. Even if it screwed over their game. If it screwed over their game, maybe they'd try harder to prepare for their game.
I no longer believe these things, for the record. That was when I was much younger and barely knew how to play D&D. But the people who taught me how to play D&D in the first place all believed that's the way the game worked.