The Germans have the great military advantage, the Soviets have the space...
Hitler just needs to not **** things up (which, with Hitler, is harder than expected)--and Stalin needs to not get couped. Without the little side distractions in the Balkans, its entirely possible that Moscow could have been captured in '41.
Possible. But it would be hard to hold it against the winter counter offensive.
Also, there could still be a Balkan distraction. The Greeks could hold out against the Italians and other minor Axis without much help.
Finally, this belongs in the "what if" forum more than here.