The magic user has better tools for exploration than the fighter, doesn't he? Fly, Scry, Invisibility, Alter Self or Polymorph to blend in with the environment, Charm Person for interrogations, divinations to solve puzzles, and no doubt other things I haven't thought of. What does the fighter class have mechanically that helps in exploration?
A layer of steel and a sharp pointy thing he is really good at using for when the dragon hiding behind a cloud decides that invisibly flying around looking like someone else is rude.
A wizard can invisibly fly around looking like someone else. A smart wizard has someone else invisibly fly around looking like someone else. A smart wizard with a good DM has someone else get eaten while invisibly flying around looking like someone else.