What about undead, though?
Asked and answered...I thought.
If there was a skeleton in the corner of the room, and you checked it for magic because you weren't sure if it was going to rise up and attack you, and there was no sign of magic but then it attacked you anyway...
Me personally? I would be like "huh? So where's its source of negative energy coming from? Maybe it's powered some other way." I would ask questions of my DM -via the actions of my character in the game world, if I really cared so much- until I had some kind of suitable, or at least interesting, answer.
But then, I would never use Detect Magic to try to detect undead. I would expect my cleric or paladin to let me know if that was something to worry about...and if I were alone and there was an unmoving skeleton in the corner...I would watch it for a minute...see if it moved or not...and then, my character would assume it is not undead. Then my character would be frightened and/or surprised when it moved to attack me...and "should I have detected magic? Would it detect as magic?" would never cross my mind because I am just trying to stay alive at that point.
That's getting awfully close to my line. I mean, I'm willing to buy that gargoyles have some sort of anti-detection magic that blocks their power source from casual detection, since that's their whole gimmick and it would be silly if a simple at-will ritual could see through it, but there needs to be some sort of logic to it. If it's all just make-it-up non-sense and there's no way to predict anything because none of it follows any consistent set of rules, then that raises a big question about why I'm even playing this game in the first place.
Well, as you said, everyone has their own tolerance. But a DM ruling that Detect Magic doesn't show a gargoyle (or an undead) is the DM's call to make. They get to decide where the "make-it-up nonsense" line is. If you perceive their reasons and rulings as "make-it-up nonsense" that's...well, just too bad, really. You can go along with it or, if that ruins the game/breaks disbelief for you, then you can bow out of that game.
I don't know what else to tell you. But individual players don't get to decide what is or is not "real/real enough/makes sense" in the game world. How magic and spells and, well, everything works is what a DM interpreting what's in the core books is for. They are the referee and arbiter. They decide.
For me, if the next time I was going into a room with gargoyles in it and my Detect Magic spamming [which would not be allowed in my games anyway] DID reveal them, then might raise an eyebrow and point it out. Or I would think "Oh SNAP!* Something's wrong/up here! Why are they detecting as magic...they didn't before." If the DM's response is "Oh right. Yeah. I forgot. Nevermind." Then we rewind a bit and carry on. If the DM's answer is "Yeah, that's weird, huh?" then the game, in fact, is afoot!
*
Ok. I wouldn't actually think "Oh SNAP" as I do not speak or think in urban-slang other than for comedic effect. But you get the point.