Why does every one invade Russia in the summer? Its a really bad idea, both Napoleon and Hitler learned that the hard way. I say invade in the winter when your supply lines are the best. Then by the time you get to Moscow (and almost every other city of importance) it is summer and your troops do not die of starvation and frost bite. This would have really worked for Napoleon because in the winter what is there to burn?
Invading in the summer when its warm was a good strategy, thier arrogance was not. Invading in the winter would surely be a surprise, however, it is notthe optimal time to invade because of the weather which in turn would slow down the advance. Germany, to be successfull, against such over all odds, factoring in the terrain, had to act swiftly. An invasion during winter would negate the one thing the Germans needed, a fast advance.
I understand what you are saying, "attack in winter while supply lines are best." I would assume you are meaning that the supply lines would be short at the onset of the attack and by the time Summer came along and the supply lines are longer, it will be easier and allow a faster push.
This is not a bad idea butthe fact would still remain that Germany needed a fast push and invading in winter would have stalled that plan. I doubt the Germans would have gotten as far as they did if launched in the winter because it would be easier to fight delaying battles for the Russians, thus bogging the German army down faster into the war of attrition which it had no hopes of winning.