But the problem with your misconception is that not all bad guys in The Road had guns, just those that banded together have guns. There's one "bad guy" that has a knife and another "bad guy" has a crossbow. And also, didn't Viggo Mortensen's "good guy" have a gun? And didn't Guy Pearce's "good guy" have one too?
Basically, when it comes to guns in post apocalyptic movies is actually quite unrealistic after a point. Look at The Walking Dead, for example. Like gasoline and prepackaged food, bullets would be in rather short supply and then completely rare (if not non-existant) after a while. In fact, though a work of fiction, Max Brooks' The Zombie Survival Guide, actually makes a valid point of this. When it comes to anything that is remotely a firearm, you might as well stop using it for shooting and start using it for clubbing if you don't have any ammo. In fact, one of his main points in the book about why using melee weapons are a better in a post-apocalyptic setting, which is that you do not need to reload it. The only other weapon that has a trigger that would be useful is a crossbow or a simple bow and arrow set. Why? Because you can recycle arrows after a target's down. Bullets you can't recycle, unless you happen to know how to make your own and reshell bullets (if you have any supplies to do so in a world where there's a limitation on all items).
Be it a world fallen under the collapse of a lack of gasoline, the zombie apocalypse, the vampire apocalypse (as depicted in Richard Matheson's I Am Legend), despite the fact you have to get close, it's best to switch to a melee weapon after all your ammo is gone.