In D&D 3.0 they introduced the average wealth by level tables, meant for assigning value to the possessions and assets of PC's and NPC's above 1st character level.
They continued in 3.5, and probably in 4e but I'm not a big 4e person so I don't know.
This was in some ways one of the best design innovations of the edition. I base this on my AD&D playing experience.
The AD&D game was quietly designed to assume that higher level characters would have access to magic items and weapons. So many monsters being completely immune to nonmagical weapons without a specified number of "plusses" being the big one. Remember, normal elementals required a +4 weapon. No amount of damage with a lesser weapon could hurt it. Also don't forget that the AD&D version of Magic Weapon was not a combat buff: it took so long to cast and had such a short duration it was really just for magic item creation.
In my experience, in AD&D, many DM's were so afraid of campaigns becoming "Monty Haul" that they handed out magic items extremely sparingly. In one case, a year-long Planescape/Forgotten Realms crossover campaign (two high magic settings) meeting weekly, lead to my Half-Elf Mage 13/Cleric 12 ending the campaign with only a Pearl of Power, a few Quall's Feather Tokens, a handful of potions and some low-level scrolls, and that's it. In another long-running game of AD&D under a different DM, my Half-Elf Cleric 11 (in a game where most PC's were around 17th level but my PC had long since hit the level limit for their race/class combo) ended up the campaign with no magic weapons or armor, and just a handful of potions, a couple of scrolls, and a plot-device xylophone that could cast Plane Shift depending on the notes played.
Magic-to-hit monsters like elementals and powerful undead were treated as nigh-invincible to fighters, you'd have to let the clerics and wizards deal with them, unless you just happened to have a magic weapon. . .then hope you have enough plusses on that weapon to count.
If a character was created to join these campaigns, even if they were coming in at 1 level below the party average, would have only starting gear. Playing a 14th or 15th level Fighter with only starting gear in any edition is quite a challenge. I always heard of AC 10 jokingly referred to as "Armor Class Mage" since wizards couldn't wear armor and magic AC boosting items were incredibly rare.
From playing through some of the "Gold Box" computer games like Pool of Radiance, by the time a character reaches 6th level a Fighter or Cleric could quite believably have a +1 suit of Plate Mail, a +2 weapon, a +1 shield, and maybe a displacer cloak or +1 ring of protection. A wizard by 6th level may have some Bracers of Defense AC 4, a +1 ring of protection, and a +1 dagger and probably a wand of magic missiles or lightning bolt. Definitely not overpowering, but definitely more powerful than any tabletop character I ever saw of that level.
Besides overreaction to avoid Monty Haul, the justification I always heard for this is that under the AD&D rules you didn't spent XP to create items, you lost permanent Constitution to do so. How many 11th+ level wizards (the point where they could be high enough level to make permanent magic items like swords and armor) are there in a setting, then how many of them would want to start losing CON points permanently to make a +1 sword or +1 shield they won't even use. Strange magic weapons like a +1 Khopesh would have the implied question of "who the heck even made this thing?"
The 3.0 and later rules at least set a guideline for how much equipment a character should have as they level up, and a yardstick for DM's to see if their game was Monty Haul, or more skid row.