My post was about the resolve of the British, the Nazis being Nihilist and prone to exterminate the populations considered as inferior. You have the same resolve by the Obama speach indicating that the Djihadist doesn't have their place in our century.
The German army of 1914 is better than the army of 1939 for sure. The french did a good fighting retreat but this is the aviation reco who save france when Klück army presented his flank and Gallieni which understood the error and benefited from this german mistake.
I'm certain there are plenty of military historians who would diagree with you on the relative quality of the German armies of 1914 and 1940 - it's certainly not clear-cut as you suggest.
Plus, whatever their relative strengths generally, the 1940 army was much better equipped to accomplish the task we're talking about - the complete territorial conquest of Russia. Far easier to say you're going to walk to St. Petersburg and Moscow than to actually do it. Even as it was, the German Army of WWI didn't seriously penetrate Russia proper until 1917. Heck, it took the Imperial Army nearly three years to cover the ground the Nazis covered in a few weeks. Even if the WWII army wasn't generally "better," it was much more mobile.
As to your point about Russian resolve, I think history has shown repeatedly that it's generally easier to predict the performance of armies than the resolve of peoples. We can't be sure at all how the Russian people would have reacted had the Czar adopted a different strategy.
Finally, and this is the real point, it would be great fun to be able to play through all of these possibilities in the game. From that perspective, this game is less robust than WWI Gold in its strategic elements (though it certainly has other advantages).