Also when you are in the usa civil war and you are given a modern day assault rifle, why don't any of the soldiers surrounding you notice?
I never understand why dev teams ignore little details like this. It is the small touches that really add to suspension of disbelief for game atmosphere. All they needed was for one soldier to say something along the lines of "WTF is that?!?" or, even better, they could have worked it into the gameplay like a bunch of union troops are about to be overrun, and you run to them and open up on the rebs with the assault rifle and they cheer you wildly.