it's all about the lens you view the game through. Right now I'm all about the narrative. Who influences it and who has ability to shape it. In D&D it is strongly suggested that the DM has complete narrative control, but then it creates spells and effects that give narrative control to some classes and not to others. It then encourages DMs to prevent the use of those spells and effects if they interfere with their narrative. It's a mess if you ask me.
In my analysis, spotlight is irrelevant. It doesn't matter how often you're the center of attention, it only matters if you can effect change in an efficient manner. The most efficient manner is to bypass the DM directly which is what narrative control is about. Moving the game in the direction you want it to go. If you want the fighter to hit better or deal more damage, you can make it happen. If you want the trip to be quicker, you can make it happen. What can the fighter actually make happen? He has no means of controlling the narrative, only in participating in one that already exists.
I want to split your notion of
narrative into two components:
situation; and
plot.
Very roughly, by "situation" I mean "the obstacle/challenge/encounter/scene that confronts the PCs"; by "plot" I mean the sequence of events that occurs over the course of play.
I don't think that D&D as such strongly suggests that the GM has control over plot. Some elements of D&D do this - especially a lot of 2nd ed advice and adventures, which encourage the GM to exercise control over "the story" - but others don't (eg there is a fairly strong sandbox tradition in D&D play, and also strong elements of 4e advice that push against GM control of plot). To the extent that players of casters have more authority over plot than (say) those of fighters - for instance, they can more easily bring about results via action resolution (say, save-or-die; or buffing other PCs) - then that just seems like an issue of imablance of effectiveness. Whether this is good or bad depends, I guess, on how important the balance of effectiveness is. 4e, at least as I see it, tries to deal with this by giving players of fighters more meta-abilities (eg enc and daily powers).
With situation, it's a bit different, in so far as different editions take quite different by seemingly deliberate approaches. 4e tends to assume a high degree of GM situational authority - players can write quests, for instance, but it is the GM who gets to frame the obstacles in the way of the PCs. And 4e drops many of the notorious rules elements (eg reliable long-range teleportation) that tend to undermine GM authority over the framing of situations. Whereas Classic D&D, with the dungeon crawl, tends to be built on the assumption that the GM will author "possible" situations, but the players will choose which ones their PCs confront. (Gygax, in the final section of his PHB, recommends the decision about which "situation" to confront - ie scouting out the dungeon to find a suitable target - as a reasonable goal for a session in of itself.)
Casters certainly have better capabilities at exercising situational authority in classic D&D - movement spells, scrying spells (to help inform choices), etc. And this seems to be deliberate. It's not just a balance issue, but seems to be part of what playing a caster gets you that playing a fighter doesn't. Changing the game to make casters more like fighters in this respect (which 4e does) is a fairly big thing. Changing the game to make fighters more like (traditional) casters in this respect would be an even bigger thing, I think.
On the "it's a mess" point - one of the bigger issues, for me, about 3E-style D&D is that with many abilities the designers seem to equivocate between action resolution abilities, which give control over plot ("OK, now my guy does this thing, and these consequences for the other pariticpants in the situation ensue."); and scene-framing abilities, which give control over situation ("OK, GM, you've framed us into an illusion-filled room, but not my guy casts True Seeing and you have to reframe us as being in a plainly perceptible room.) Divination spells are particularly obvious instances of this, but so is the Diplomacy skill (reframes from social conflict to NPCs as non-obstacles), the Perception skill (use much like True Seeing above), and other abilities too. Teleport is another instance too - it looks like it could be action resolution (say in a game like MHRP, which permits the challenge to be framed as one involving vast galactic distances) but in D&D, which really has no action resolution mechanics for dealing with conflicts beyond skirmish-level ranges, it defaults to scene-reframing.
It's not necessarily a bad thing to have abilities that straddle action resolution and scene-reframing, but it's seem a mistake to include them just by accident.
I guess that's just part of the D&D charm. It really only creates problems for players who want more influence over the narrative and haven't found a DM who wants more player narrative control. Is that segment significant? No idea.
My guess is that it's not that big a segement. [MENTION=6688937]Ratskinner[/MENTION] has views on this, too.
In the story of the game, magic items may come from spellcasters, but in practice they come from gold pieces - and (in most groups) that is a resource shared equally. And even if the spellcasters do the magic items and buffs, I find it is having the spotlight that players compete about - and the buffee, not the buffer, gets the spotlight. In the same way, the user of amaiig item, not it's creator gets the spotlight. Ans spotlight is a big part of narrative balance.
In 3x magic items tend to come from wizard XP and spell memorization, at least in my experience.
I agree with Starfox to the extent that items earned/acquired from NPCs aren't a burden on player authority.
I agree with sheadunne that if they're a gift from another PC that can make a difference - though in a Rolemaster campaign I ran one of the PCs was a (non-magical) crafter (of weapons and armour) but only ever crafted for other PCs (he was at the bottom of the samurai hierarchy within the party) and I don't think the players of those other PCs ever felt overshadowed because their uber weaopns and armour had been built by another PC.