The arbitrary "1 million sales" figure has mostly been promoted by people when they were trying to argue that a game for a HD console that sold a million copies but bankrupted the developer was successful while a game for the Wii that only sold 500,000 copies but received a sequel and was the most successful game for that developer ever was a failure.
Many publishers and developers (EA for example) effectively claimed that HD console games cost 2 to 4 times as much to develop as similar Wii games; and by similar they don't necessarily mean just that the genre is similar, but the scope and size of the project is similar as well. For many moderately big budget games on the HD consoles 1 Million sales (across all platforms including the PC) would only represent a small fraction of their development costs, and for many moderately small budget games on the Wii 1 million sales would represent several times their development costs.
