I always found the magical economy of 1e and 2e absurd. The party fights a patrol from Zhentil Keep or the leader of the mercenary band and ends up with a bunch of magical loot. There's a +1 battle axe (that nobody's proficient with--the fighter blew all of his proficiencies on longsword, weapon specialization, two weapon fighting, and longbow proficiencies), a +2 chain mail (the fighter and cleric have plate mail already--and that's better), a +1 shield (did I mention that everyone is using Two Weapon Fighting?), and a bunch of scrolls. So what does the party do?
They go into town and sell the items they won't use (chain mail, battle axe, shield) of course. There's a convenient gp value listed in the DMG to let you know how much the 50% value that PCs get for selling items is. Then they use the gold for training, castles, horses, etc.
But if the PCs looted an ogre's horde and fount lots of gold but have no magic, can they ever find anyone doing what they'll be doing in a couple of levels? Of course not. You can't buy magic items silly; you can only sell them.
But take a different tack. Suppose a PC establishes a stronghold and attracts his nifty followers. Now he's got a bunch of drow equipment that he stores in the basement and uses to equip the night patrols so they're set. But what about the day patrols. If they run into gargoyles, they're hooped. So he wants to get them some magic swords and a few scrolls for just in case. It can't be that hard--after all the Zhentarim do it. But lo and behold, what is obviously possible for NPCs requires PCs to forge the blade from meteoric iron and crushed dragon bone in the fires of hell, quench it in the river styx. And the scrolls? Mark off two years and find howler quills, medusa blood, and harpy skin to write it. And if you're still alive you'll get your scroll of fireball.
After noting that greatswords and shields were both actually worth using and that there's now a workable system for doing something outher than killing people, the first change I noticed in 3.0 was "hey, now PCs can make magic items too. It's about time!" And when I found that there were rules for buying items, I was glad to see that covered. Finally, someone other than the PCs was selling items they couldn't use instead of hording them in the basement or using them for fenceposts.
All that said, I don't like the degree to which some people have taken buying items. "A merchant shows up with a cart full of magic items--what do you want to buy? He's got it all." That rather takes the fun out of it. However, visiting the wizard's guild and finding an apprentice hawking scrolls of detect magic to cover his tuition and a journeyman who'll enchant a cloak to +1 in return for money to buy a library, going to the temple and offering 5 bulls and pounds of incense (as well as a large donation of gold) for the priest's use in the ceremony that adds the Holy ability to your sword, or visiting the seamy side of town and talking to someone who can "aquire anything you want... for a price" add to the game immensely.