France likely surrendered because their home country defense force was defeated and their capital overrun, the countries administration had little chance of extracting itself from the rest of France before being completely overrun.

This does not always mean surrender; think Napoleon's invasion of Russia. The difference for Russia in my opinion is that they had a large homogeneous land mass upon which to move and maintain their administration.

I think it was the large number of casualties the soviets were wiling to tolerate, I doubt the French would have encouraged the loss of a million as was incurred during Stalingrad. Consider also that the large land mass was a liability as it had to be defended, for example from Japan.

The USSR had time, resources (human and material) and the land buffer to keep fighting. The farther Germany pressed into the USSR, the more Germany's resources and supply lines were stretched and the Soviets eventually realized that.

Similar reasons cost Napoleon dearly ~130 years before.

Also, Stalin's massive ego wouldn't allow a city named after himself to be taken by the Germans. That's the primary reason that particular city suffered the high casualties that it did. Stalin once told Churchill at the Tehran Conference that "when one man dies it is a tragedy, when thousands die it's statistics."[1]

[1] http://books.google.com/books?id=8fp1A2s6aQwC&pg=PA510&dq#v=...

Well, in World War I the French did have 1.3 millions casualties. But there the French leadership did not face a situation were the war seemed hopelessly lost in the face of rapid German advances.

But the distinction is that its wasn't the potential of losing Paris and Parisians that forced France to surrender. The French government judged that they had more to lose than gain from continuing to fight.