Exactly this:
A wizard can switch up his spells based on the situation. He can have an exploration spell mode, a social spell mode and/or a combat spell mode. Note the wizard will still, almost certainly, have enough spells available (prepared) to be just fine in a fight or social situation, even if that's not what they prepared for (for ex. suggestion is great for combat AND social situations). Magic items are gravy and allow the wizard to devote less resources to a given area (for ex. the staff of defense).
Fighters, on the other hand, get what they get and that's it. If a fighter wants to be good at exploration or social rather than combat, they will have to devote a feat (if they're even allowed) or a maneuver, both of which PERMANANTLY subtract from the fighters ability to perform in another (the non-selected) area, usually combat. I think maneuvers can be swapped out at certain levels, but that's still a HUGE commitment. So the fighter is utterly reliant on finding magic items to shore up the gaps - but these are at the whim of the DM.