I've noticed in PitF and GTC, soldiers don't seem to break as easy, nor surrender as often as previous versions. Given the time of these battles, wasn't the Wermachts' morale at a low, thereby resulting in more soldiers surrendering?
You would have to play a campaign in GtC to see that. You will see lowering morale of the units the longer they are engaged with out rest, and the few replacements you'll get will for the most part be inexperienced, which if left alone outside a commander's command radius, will break very easily.
In Pitf however, the high lethality of all the weapons make the act of surrendering a bit of a strange occurrence.
As for the historical morale of the German forces during these operation's time frames, I don't know, maybe some one with an historic knowledge could enlighten us.