Yes, game-mechanics wise, there is very little to recommend fists over guns or weapons. You can't accidentally kill somebody in DFRPG, fists flat out do less damage than weapons, and weapons can grant special aspects etc.
But story wise, using the Fists skill can make all sorts of sense. First, its one of the few combat skills that "civilians" might train to high levels. And as mentioned, bringing a weapon with you is often considered rude, or can get you in trouble with the cops. Also, you don't always want a weapon in your hands during a fight; fists leaves your hands free for anything you like (such as grappling, taking the enemies weapon away, picking up the McGuffin, etc).
Even mechanics-wise, fists aren't so bad; you don't hit any less often, and only do a bit less stress with each hit. If you have some maneuvers to tag, you can still stack up quite a hit. And since you often have to draw on the first attack (-1 supplemental action) to use a weapon, which might cause you to miss, the gap is smaller than it looks. As long as you have a strong defense and don't let maneuvers against you pile up, you can wear the enemy down; your fights just last a bit longer than they would if you used a weapon. And story wise, that can be a good thing!