D&D and Rolemaster, the systems I'm most familiar with, place treasure by monster type. The various retroclones I have seen either copy the system exactly, or rename it and move its bits around ("Hoard Class" in Labyrinth Lord, for example).
The basic idea is, certain monsters have certain types of treasure, regardless of where you find them. But generally, the really powerful monsters are found deeper down in the dungeon. So you go deeper, fight tougher monsters, and get rich if you survive. But what the monster is, and how wealthy it is, is more important than where it is. A dragon on level one is still going to have "H" type treasure.
Video games, even pretty early ones, tend to tie rewards to location more closely. You find more money and more powerful magic items in the final dungeon than the first one, or deeper in the big dungeon, or closer to the end of the story.
GURPS Dungeon Fantasy doesn't have a treasure system per se. It has a whole random treasure generation system, but not one that decided how much is where, or what monsters have what treasure. It is left up to the GM, although it does provide some guidelines on what giving a PC a certain amount of treasure can mean, in terms of real in-game power.
So as the GM, with my own ideas of how my game should go, I pretty much had to decide how to hand out treasure myself.
Instead of deciding what monster gets what treasure, I simply decided the deeper you go, the more treasure there is.
The deeper you go the tougher monsters get, too, but it's the level of the dungeon (either in a literal, physical sense or just as a definition of danger and reward) that determines what you get. Deep in the dungeon, there is more money. Near the surface and easy access points, less.
I've given bonuses and penalties based on the strength of monsters - a boss-level monster will likely be wealthier than fodder. I've also set the dungeon level both literally (level 3) and figuratively (this one should be tough, I'll up it by +2)
Once I figure out how much money they have, I can set the type of wealth based on the creature - gargoyles with gems, dwarves with gold, etc.
My system isn't ready for prime time yet - it's still in alpha testing with my own game.
It's worked out with both good and bad points.
The Good Points
- it's compatible with DF8, because all you need for that is a total to build up to.
- the deeper you go, the richer you get. Not only do monsters get tougher the deeper down you go, but the treasure gets more valuable. Not automatically - a bad roll can mean a poor find even pretty deep - but generally. Plus big hordes go from outliers on the bell curve to pretty common occurrences.
- you must go deep, and risk a long journey home, to get rich.
- it's easy to adjudicate. It doesn't matter what the monster is, just where it is and how tough it is.
- it's hard to be a rich guy living on level one. If you're close to the surface, you are unlikely to be wealthy. This means you can assume a tough target on level one somehow is a weaker version, hasn't had a chance to accumulate a horde, or has been mugged on the way down or something.
- It's easy to be a poor dragon. The lack of a direct tie to monster type means a dragon on an upper level of a dungeon is more likely to be poor than one on a lower level.
I deal with the reverse by scaling up monsters by level, so while a goblin down on level 10 would indeed be rich, it's impossible to roll up a goblin on level 10 anyway, so it's a non-issue. But it's not impossible to get easy foes with extreme wealth or nightmarishly tough foes with little or no wealth.
But as a basic approach to placement, it hasn't worked out badly at all. Go deep, fight tough monsters, and get rich.