Lord Fyre wrote:
(Yes, I am an American, worse I am a Californian.)
A Texan, a Californian, and a Washingtonian are at a hunting camp together in the woods. They're sitting around the campfire drinking when the Texan suddenly stands, throws his bottle of whiskey into the air, raises his gun and shoots it. He then sits back down. The other two look surprised, so he takes out another bottle from his pack, grins, and says "We've got plenty of whiskey in Texas."
The Californian laughs and stands up. He tosses his bottle of wine into the air, raises his gun, and shoots it. Then he sits back down, pulls out another bottle and says "We've got plenty of wine in California."
Finally, the Washingtonian stands up. He takes his can of Olympia beer and tosses it high into the air. He raises his gun and shoots the Californian. He then catches the can as it falls, chugs the beer, and says "We've got plenty of Californians in Washington."
Brilliant! My friends in Seattle would be amused.
The reason for the commoner class is to have someone that is semi buff that doesn't have specialized skills he couldn't justify. Not everyone in life is a highly trained specialist in a skill (expert) or in arms (warrior) and certainly not in a PC class.
Sure, once you get to 10th level it's all noise. But for people that do a lot of low-level gaming, it's very handy. Those three farmboy brothers down the road are known for getting drunk kicking people's asses they don't like and are L2 commoners. You need a level or two under your belt to cross them, maybe. Their farm can be close to orc country plausibly as they can run off a solo opponent. It gives you a way to do the "American pioneer" kind of freesteader who can get along a little out in more wild areas without being good with platemail or having a masterwork-level craft skill.
You don't have to have peasant levies in your army, but if you do they're certainly commoners.