Exactly. Why is it that "Magic items are supposed to be priceless and rare", but you can go into any local dungeon (there always seems to be at least one near every small town, and probably a big one near every major city) and beat up a few lowly orcs and skeletons and come away with a some +1 weapons and a small wagon-load of treasure.
D&D before 3e always had the dichotomy that making magic items was supposed to be insanely hard, permanently draining to your Constitution, very time consuming, and could only be performed by at least 11th level casters (except for scrolls and potions, which could do it just a few levels earlier), in a system where 11th level was a lot harder to achieve. So Magic Items are supposed to be rare and powerful?
Then why were they absolutely everywhere? Why were the treasure rules so stacked that 1st level PC's had a fair chance of getting magic weapons, armor, and a good supply of miscellaneous items and scrolls and potions by 4th or 5th level. Published modules always seemed to be swimming with magical loot, and I've seen PC groups have to literally take wagonloads of treasure (mostly coins, but a fair amount of magic items in there) away.
Also, the inherently ad hoc nature of 1e/2e item creation was so easily broken. To make a potion or scroll you just needed rare items from monsters or the like, which smart PC's almost always found a way to "farm" them, then they could have all the items they want. A standard gold & XP cost on creating items at least ensures that making items always costs PC's something. If you want the flavor, replace the gold cost with items they have to buy or adventure to get, but make the items have appropriate value to the GP cost.
The game always presumed you would have magic items, after all, most high level monsters required plenty of "+'s" to hit, and if you didn't have magic weapons as a high level fighter, it would get ugly since they could ignore 1,000,000 points of "normal" damage.
3.x's Magic Item system puts them all on a level playing field. If you want a Mighty Doodad of Smiting, it will cost you "X" amount of gold and "Y" amount of XP to make. The GM can scale it up if he wants a lower magic game, but there is a uniform base for campaigns to build on to establish how hard magic items are supposed to be to make.