Having energy weapons included in common weapon skill doesn't need to have anything to do with realism and wondering what kind of sights each gun has. But if it's so important, then let it be stated that once you're good at shooting, you don't always even have to look through the sight to aim properly. And once you understand the mechanics of guns in common, it's much easier to shoot and maintain new weapons.
The actual point was if firearms skill consisted of energy weapons, then those guns could be rare or mostly provided to the members of certain faction like enclave or Salvatores. It would also balance the pvp requirements because right now being a big gunner or energy weapons user, you get less "pvp rounds" because it's harder to craft those weapons.