Obryn
Hero
I definitely think they're less central than they were in 3e, but it seems to me that magic items have been vital for most of the life of the game...The placing of magic items in the PHB just seems at odds with the premise that one of the 4E design goals was to get rid of the dependence on magical items. It just seems a bit strange that magic items appear in the PHB as if they were standard equipment for the first time in an edition that claims to reduce the need for them.
In 1e/2e, you had the all-powerful Girdles of Giant Strength and Gauntlets of Ogre Power. No self-respecting Fighter or Barbarian went without one.

There certainly wasn't a magic item shop, but in my memory (at least), magic items were quite important under 1e/2e - in fact, they provided a lot of the mechanical differentiation between characters. They were hugely vital in 3e - particularly for non-casters. They're much less vital in 4e than they were in 3e, but I still don't think they're down to the 1e/2e level.
As for what book they're in... For a 3e or 4e style game, I like having them in the PHB. By the time you're making higher-level characters, you need to have access to magic items. Also, in any game which lets you make magic items (both 3e and 4e), the players need to know basically what they can make. Putting them in the PHB means players don't need to buy, beg, borrow, or steal a DMG.
For 1e or 2e, where PCs didn't ever make magic items, and where magic items were seen more as "loot to find" instead of "stuff to buy/make," having them in the DMG was great.
-O