Just some reasons...
1 - US - confidence, good Support lines etc.
Germans - Desperation, the sheer German stubbornness not to give up, the fear what the Soviets will do to the German Civilians...
British - Younger and younger recruits, nobody wants to be the last men to die in WWII etc.
Soviets - Overall bad Training etc.
In addition I am always looking up other WWII game Systems, like BA, DH or FoW to get a bit of coherence across game Systems. So even if I read a historical text about well trained Soviet Units but the Overall gaming Consensus are badly trained Units, I tend to give also less exalted gaming stats.
I am afraid I do not really get your question…
M1919A6 .30 Cal HMG 3 48” 2xD6+1 Set Up/2, Suppression
M1918 BAR 3 36” 3xD6 Suppression
Bren LMG 3 36” 2xD6 Set Up/2, Suppression
Vickers HMG 3 48” 2xD6+1 Set Up/2, Suppression
Looks different to me, can you explain it a bit more?