Inertia should also apply to turning while aiming a weapon. It's just not as easy to suddenly change your point of aim with a weapon in real life as it is in the game.
It does apply in-game. Try changing your point of aim in prone, then try it standing. Try it with a pistol, then try it with a rifle. Swivel a light MG, then swivel a heavy MG. There's plenty of inertia. Try it in practice mode or campaign.
In fact, people should test out all their assumptions before posting about them. Experiment and test everything. Just go into the console and type "open TE-mapname?minplayers=1".
In reply to Maraz, you would be correct if Stalingrad was a typical World War Two campaign, where the soldiers carried combat loads well in excess of 60 pounds (though the Soviets mandated a 40-pound maximum in 1945 during the final months of the war).
However, soldiers in Stalingrad moved light. Assault squads often carried little more than personal weapons, a helmet, and a canteen. See attached pictures.
This is reflected quite accurately in RO2. Just look around at dead bodies and your teammates--only riflemen, engineers, and AT soldiers carry packs, and riflemen carry only light field packs (or a sack tied with string if you're a Soviet). The AT soldiers and engineers do carry more, but guess what? They do move slower, as do machine gunners.
Assuming a ten-pound weapon, twenty pounds of equipment and ammunition, three-pound helmet (all Germans and some Soviets), and two to four pounds of grenades, that adds up to about 40 pounds of gear, spread out with ten pounds in your hands, thirty-five or so on your back and belt, and three on your head. Hardly crippling. Soccer players might be an imprecise analogy, but the point there holds true.