As a DM, how and why I place treasure hasn't changed in the slightest since the 1e era. Third edition crafting rules didn't change anything for me really. I just expanded my game in to the ambiguities and details of the system, and despite having some objections as to the pricing system, generally felt comfortable and at home with the addition of a formal system.
1) Generally speaking, magic items of the sort useful to adventurers not purchasable. The exception is that readily craftable low value items like potions and scrolls (which were comparitively easily craftable even 1e) are readily purchasable in large cities from temples, hedge mages, and alchemists. Such items could possibly be commissioned from wizards provided one with the suitable skills could be found, and a friendly relationship with that wizard established, but this would usually involve several quests both to gain the wizards trust and to obtain the necessary regeants for the work. In my game world there is also a merchant guild that specializes in dealing magic items and other rare arcane goods, and they hold monthly auctions, but such auctions are secret, invitation only affairs, held in major metropolises only, and involve me making 2d4 random rolls on a treasure table. Buyers are often powerful, wealthy, and out bidding them for rare items generally earns you an enemy willing to kill you to get what they want. Even this most well connected merchant house can't gaurantee a particular item is ever available.
2) You can, if you have the skills, make it yourself, but this requires knowledge of a 'recipe' and obtaining certain rare ingredients. Though a large market for ordinary spell components and reagents exists so that your gold is probably effectively fungible if you are making a potion of cure light wounds, rare ingredients for powerful items generally aren't available on the open market.
3) Items are created and placed primarily with thought to what makes sense within the game world. The tomb of a wizard probably doesn't contain a magic sword, and may not contain ANY treasure unless culturally it was considered appropriate to bury a person with their most valuable possessions or some other in game explanation exists for why there is treasure down there. Likewise, some reason why the tomb hasn't been robbed of treasure must exist. If the treasure is easy to obtain, chances are someone would have already obtained it. So if the tomb DOES contain a magic sword, it's probably the possession of a tomb robber and nearby will be the trap or tomb gaurdian that did him in.
4) A certain amount of treasure is randomly generated because I feel that true randomness generates a more believable range of treasure than if I choose everything.
5) A certain amount of treasure is designed to have immediate use to the party in general and particular characters specificly. This is justified on two levels. First of all, it is assumed that the characters are not so unique that their needs and desires aren't common to a large portion of the adventuring or heroic class. Therefore, most of the powerful items that have been created were created specificly for people very much like the adventurers is skills and needs. The magic sword of the tomb robber is therefore very much the sort that a tomb robber with a rogueish skill set would have desired to have. Since my general rule on powerful treasures is to give out small amounts of above average items rather than large amounts of subpar stuff, and since I'm fairly good at ascertaining what a player wants, I'm usually pretty good at wowing a player with something better than he expects without unbalancing my game.
For example, I recently placed a Eager Keen +2 Rapier of Swiftness which was inscribed with the name 'Firstblood'. The rogue in the party was very pleased. It's awesome treasure, especially given the average character level in the party right now is only 4th. But, on the other hand, it's only a +2 weapon and its probably going to be the best item available until the character is 12th level or more. It's expected to last basically his whole career. Better yet from my perspective, the item is one which I can and intend to elaborate on over time. The item is subtly cursed, and the character is going to unlock 'powers' - good and bad - as he levels up and has he fulfills certain prerequisites (like spilling innocent blood). Allowing items to evolve has a long history in the game (see Ring of Elemental Command, Artifacts, etc.), and its nice because a lot of people tend to build 'relationships' with inanimate objects.
Secondly, it's justifiable on the metagame level because I as the DM have some obligation to ensure that somewhere out there are the resources necessary for the players to overcome the challenges I intend to present them with. The game is more fun for me as the DM if the players can win, and indeed most of the time do win. Therefore, it rewards myself to reward the players with the sort of things that they need. They don't need to give me a 'wish list', because I know even better than they do what they really need. What they want is a less important consideration, because players often want more than they actually need, or desire things that allow them to overcome every obstacle in a straight foward manner. But ultimately, this may be less fun for them than making do with less. The more mature sort of player recognizes that getting everything they want, makes the game 'Monte Haul', and less rewarding thereby and so they expect and desire me to make it tough on them.
To the OP I would say, it is apparantly your experience that magical treasure is never very exciting. But, however real that experience is, it's just one perspective on the game based on one sort of experience. In my experience, I've never had a player that wasn't excited about magical treasure, and while I've found a lot of treasure as a player that was merely ho-hum, I've also found a lot of treasure that was just awesome and became almost character defining me. Indeed, it wasn't that unusual in dungeon crawling centered games for your character to be defined as much for the stuff he carried as his personality. Some of my most favorite treasure was never findable on any treasure table or list, like the short sword +3, detect magic x3 daily with the periapt of proof against poison built into the pommel.
He's loving it.
