It occured to me that in previous editions of the game, some DMs tried to do some balancing of well the non-spell caster with the caster by giving the unempowered ones items that were both powerful and highly flavor defining for the character...King Arthur isnt himself without Excaliber. The problem was they were a bit overwhelmingly so the character didnt feel special except with this item and the acquisition of which was completely under the DMs jurisdiction.
The acceptabilitiy of these "character defining items" or even "character defining magics" for me is directly based on how player controlled they are.
Basically an item can be more important to a character both in terms of defining there abilites and acting as the basis of his power if the player has more say in its nature and certainty of its inclusion in the characters story.
The trend I have seen and heard in 4e is towards making items less defining by using inherent bonuses... without inherent bonuses item based power seems too great... Items with big themes and lots of powers and lots of impact on the characters power... are fine if they are literally a player resource.
Legend and fantasy give us both heros like lancelot and beowulf who may have had magic items but who's personal awesome totally over shadowed them ... and we have arthurs and elrics who conversely were probably either highly item dependent or overshadowed.
Allow the same resource spent for personal awesome to be spent for magic item awesomeness.. You could do this by defining a theme or paragon path in terms of magic item awesomeness... Fated Weilder would make your character the bearer of insert Item of uberness X which they determine to be part of there characters story... its no longer an item that can be lost or stolen except temporarily its nature is something the player can design perhaps you could spend item specific feats on it...
However maybe that can be done already.
OK I admit it I do think a healthy dose of flexible imagination solves everything. See the player is welcome to explain how any of his advancements occur ... where did you get those new rituals or that new battlefield spell oh wizard ? and why does the character get a white lotus riposte from his eldritch strikes? Perhaps its that new magic sword that is responsible (is it the source or did it just awaken that innate gift?). This can be done with any character design feature .... I didnt learn to do ritual magic the skull with runes painted on it I tote about possesses me and I can do deep magics because of it.
Some people moan about players feeling entitled to there magic items.. I say they should be.