Crysis is a bonafide showcase for Windows Vista and DirectX 10, which will make many people upgrade just to play the game. When Tomb Raider and Quake came out with support for Voodoo cards, people just went crazy upgrading their PCs and bought the game to showoff to their friends. I feel Crysis is that type of game.
A million copies may actually be too bullish. The selling point of this game is cutting edge DirectX 10 graphics on Windows Vista. There might not even be a million people who can run this game.
Games like these don't sell many copies...studios putting out games like Crysis are more likely just trying to show what their graphics engine can do at max so they get other companies to license their technology.
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