While I agree that balanced classes shouldn't upset people who don't care about balance, the issue is that designing balanced classes isn't always easy, and sometimes efforts to balance classes (or monster powers, or whatever) ruin the feel.Balanced classes will make those want balanced classes happy and should not really bother those to whom it is not an issue of importance.
It should also be mentioned that it is not necessary for balanced classes to be the same as one another. Fighters can still be fighters with all the advantages and disadvantages that come with that class, Mages can still be mages and so on. Classes can be (and should be) very different from one another and still be relatively balanced.
For instance, 4E's Fighters do (arguably) feel like Wizards, with their daily martial exploits that feel (at least a bit) like Vancian spells, and medusas that don't actually petrify with their gaze don't feel like the Medusa of myth, etc.
Good game balance doesn't come free, so going for balance can cost you something in other parts of the game.