But, to be frank, I don't see much difference between the wishlist approach (which is what I assume you mean by "DM providing")...
... and the purchase approach - it is merely a question if your stuff on order is delivered during adventures or between them...![]()
There are also player-perception reasons and how player's value of items can changed based upon how they receive them. In my experience, a player who goes out and buys a magic sword from a magic mart thinks differently about the sword and his position on the Wealth by Level chart than one who receives the sword from a powerful patron. And he, in turn, thinks and acts differently than one who finds said sword deep within a dungeon.
My apologies for anecdoting...![]()

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.