It's not a genre convention, it's a nod to playability and ensuring that characters have a good chance of facing level-appropriate challenges. It BECAME a genre convention because, after being used for a while, people realized it worked really well.It is a genre convention in older D&D that more dangerous things exist on deeper dungeon levels.
And I would argue this is a perfect example of the world conforming itself to the needs of the characters/players rather than the world conforming itself to the imperatives of the world. While the tougher, bottom-level monsters didn't change their nature if lower-level PCs encountered them on their level, they also didn't roam around, changing levels in the dungeon so that 1st level PCs met the Balor that usually lived on the bottom level of the dungeon while he was upstairs on level 1 looking for a tasty Kobold snack. Are you honestly proposing that every dungeon in the game world having a top-weakest/bottom-toughest hierarchy was a "natural" design choice rather than an articifial construct based on accomodating the ability's of the characters?Reynard said:But if the 1st level PCs find the stairs down (and they often did because there tended to be multiple points of entry to each level) and they hit level 2, the creatures on that level don't suddenly change "CR" to accomodate the PCs' level. More to the point, the dungeon exists in its state, with weaker monsters up top and more powerful ones deeper down and the PCs have the freedom to (attempt to) move about those levels as they wish.
