WW in the game is mostly for balance I think. But even looking at it from a practical point of view, I still agree with it. The more prosperous a country, the less it will want to initiate a war, which is how it works in the game IIRC... But like I said, mostly for balance.
Tell that to some of the Apolytoners who are more adverse than any Afghan rebel or Viet Cong has ever been.'Ol Sid and Civ team...the war is over guys, forget it.