Well let's see....
If you don't mule, and the Soviets do an orderly retreat without standing their ground too much, whether carpet or checkboard, Germans can't encircle or do enough damage to either to the Red Army or the production centers before they are shipped out.
If you can't damage either, you face a huge army, made worse by the massive impacts of the blizzard and now the 1-1 becomes 2-1 rule, leaving the German army absolutely incapable of doing much in 42. This is my third game against a good carpet/hedgehog, without muling, and the same results are happening repeatedly. BigAnorak says that a war of attrition can work and for him it is, but I haven't seen his early turns to figure out what he did in 41 or what his opponent allowed him to do.
Throw in that FOW is too extreme in this game, hasty attacks only allowed from a single hex, and no true probe or recon type attack to determine the contents of the hex and the games nothing but frustration for the Germans. Who on earth wants to play a frustrating game?