It's more of the result than anything. They were still a century behind prior to the war. Stalin still had not unified the country. The outcome was a national victory, Russia as a major world power, and the economy coming out of the stone age. It was a coming out party for Russia as an equal and the people (in general mind you) were unified.
It's a way to really unify the country - those who hated the Communist era still have nationalist feelings. So across the board it is sort of the token "remember" concept. I guess the closest we have is 9/11 and it seems to have lost its luster.