@Tony Vargas I agree that 4e is best read as having the intent that magic items will, at least typically, be 'build elements'. I am just not sure it absolutely follows that PCs are intended to be able to easily trot down to the Magic Mart and pick up a Staff of Ruin. I think the 'quest model' is closer to what was intended. The idea of 'wish lists' sounds a LOT more like facilitating that than anything else. The players provide a list of items THEY think would be cool to have, and then GM is enabled to work relevant and interesting treasures into the story instead of just giving away whatever they feel like or whatever happened to be listed in some horde listing in Module X, Room 42.
4e actually does NOT encourage purchase or make that much at all. Yes, it is easy enough, in theory, to make items, but it requires residuum (basically gold) and then precludes all the ways to amass enough to do so! Only 10% of all treasure is money by RAW, barely enough to enchant a few less critical items. If you try to sell/disenchant, you get drastically less than the item is worth, and thus cut into your overall power (IE you can have 3 good items or one that is the perfect item for you, take your pick). Buying, as I said before, also has an ADDITIONAL 'overhead cost' of 10-40% by RAW, making it the worst way to acquire items.
You can definitely buy items by RAW, but you will do so maybe only a few times in your character's career, if at all, and that isn't even factoring in that the GM is not obliged to make any arbitrary item available or put the seller in some convenient location.
Finally, with the rarity addendum WotC pretty clearly put a LARGE swath of the more specific items out of bounds entirely.