Well, if you want to use mechanics for the narrative: the tieflings have plenty of fighters. If, as aplayer, could command four of them as my party & equip them at the smith, I could easily clear the goblin camp with them. The player's party is not needed. So Zevlor's story is a fabrication as well; they could fight their way through, but instead lie that they cannot.
These things don't really "exist" in the world, they're just here to make playing less cumbersome. It would be nice if the mechanics reflected the world, but convenience trumps everything in modern gaming.
I agree. While I'd prefer more attention to detail, I am not interested in playing an inventory simulator game either, so I tend to overlook things like merchants having infinite gold or stashing 10+ weapons and armor in your backpack.
