Strikor, the allies used any weapon avalible. My grandpa was 101 Airborne, he tole me that when in battle they'd take any weapon they could find, weather it be Kraut of not. Thats why alot of the size bullets are the same, to be almost universal. Also check out modtheater.com, they interviewed Dogmeat and he had a really good reason why EA didn't realease SDK.
there's a difference between taking any weapon avalible on the battlefield and having an unlimited supply of german weapons, why couldn't they simply make a portable .30? if their excuse is that it took more than 1 man to set it up then i dont really see the point of vehicles.