On Scaling Monsters

Lately I've heard, "I can't use monsters for more than 5 levels because they stop being a threat to the PCs." I've seen variations on this, but apparently many D&D and other level-based system GMs feel like monsters have an expiration line that reads "use by level 7".

Ceci ne pas un checklist.
Seriously.

As the PCs level up, some fantasy games fall into a monster progression that reads like a Who's Who of the Monster Manual. It starts with Kobolds and Goblins; then mid-humanoids like Orcs, Hobgoblins, and Gnolls; then Ogres and various flavors of Giant; and finally Big Scary Critters like Dragons, Beholders, Mind Flayers, the Tarrasque, and other unique challenges. "We can mop up the remnants of the Orc army, but now you need to hunt down the Githyanki that supply them and figure out their motivations for doing so."

Why?

If you accept the conceit that the PCs are going to get harder to kill as they gain experience, why limit yourself to thinking that the monsters they fight will stay the same, even relatively weak creatures like Goblins and Kobolds? Granted, any army will have a large contingent of unwashed zero-level conscripts regardless of race, but once they survive a few battles, won't they improve their survivability and capabilities?

I'm a big advocate of listening to the game world and learning what it needs. If you do decide to introduce a new race just to provide a new challenge for the PCs, where does that race fit in the game world? Who are they in conflict with and how have they survived this long? And can your players play a member of that race? Do they exist for a reason in the story of your world, or are they an after-market hack job to challenge your PCs?

"The spear's just for show."
*Meteor Swarm*

Why enforce an artificial progression of fantasy critters that don't exist in your world when you can retool a few basic races and power them up to provide higher-level challenges? Why don't other races take a page from the PCs' playbook and create troubleshooting teams? Why aren't there Kobold Archmages? Goblin Grand Druids? Orc Warlords and Warlords-In-Training ? Hobgoblin Monks? Adventuring parties who happen to be non-PC races?

Yes, it will take some work to get usable stats on these leveled-up monsters, but that effort pays off in a more consistent world for your players to explore. Plus, a high-level party will never be sure sure about engaging a small group of humanoids. And that's the way it should be, I think.

"Whaddaya mean the goblin gets a Wish?"