(Warning, I have a tendency to get long-winded):
I hope by now it seems evident that the game has always presented two different realities to the player base. The rulebooks seem to indicate a "typical magic" setting where the heroes stand out for being adventurers with abilities beyond those of mere mortals. Magic items are uncommon, and NPC casters (while they do need to exist) are relegated to major cities and are not terribly inclined to help you without persuasion.
The adventures and settings, however, present a world where the players are not out of the ordinary. Adventurers are a known quantity, and NPC's with class levels, as well as spellcasters, appear with relative commonality. Magical items are strewn about as needed (I mean, even Keep on the Borderlands had low level NPC's armed with weapons and armor +1 fairly liberally). I surmise this was an attempt on the part of content creators to prevent the PC's from becoming lords of the setting, able to impose their will upon the populace willy-nilly (and by the 2e era, at least, I at least noticed some disdain for "0-level NPC's", especially once Non-Weapon Proficiencies established themselves as the standard (despite being labeled as optional in the PHB).
After all, it's hard to have a master weaponsmith with multiple proficiency slots devoted to his craft without answering "hey where did he get all of those proficiency slots anyways?".
We like to say that "magic marts" don't exist, but you can find so many examples of them that I'm fairly sure I saw a product devoted to one and explaining how the wizard avoids being robbed and swindled.
This of course, creates a disconnect among the player base, where they can cite examples and facts at each other that are wholly contradictory. Gary would say that nobody has an expectation to find "rare" magic items, which are so uncommon that they will never be found for sale, then writes an adventure so chock full of +1 long swords and potions of healing that the players start thinking about going into business selling the darned things!
(I know his intent was for the party to arm their hirelings and henchmen, but even though "name-level" characters still could attract followers in 2e, I can count on the fingers of one hand how many times I saw someone who wanted to do so in the first place. The players had decided base building, wars, and politics were way less fun than running around in labyrinths gathering loot.)
And yes, an unfortunate circumstance of this is that the world sure feels a whole lot more magical than is claimed, thus begging the question of "hey, if the mayor is a 7th level Fighter with 18/59 Strength and +2 full plate, why is he paying us to go deal with some bandits?".
Let alone the question of how a 20+ level character can't make a party of simulacrum adventurers to solve just about any problem that comes up!