I think it goes to the spirit of the game. These are soldiers of the German army. The Nazi party was a political party deeply entrenched in the military.
I like the separation between Nazism and the soldiers fighting on the ground. It feels honest, like they're being treated as people instead of mindless kill bots of the Nazi regime. And while it may feel dishonest to imply there were no Nazis in Stalingrad, I think the reverse is just as bad.
As one of the German officers put it in the movie Stalingrad "I'm no Nazi." Yet they were there fighting for the Wermacht. To me it's good that, for once, the censorship of WW2 games actually had a positive outcome, by making the game a conflict between soldiers, not really a conflict between good vs. evil. I can actually sympathize with the Germans in Stalingrad, something I didn't expect when I decided to buy the game.