My friends, whom I (admire deeply) some examples...
World Of Warcraft (12-20 million) + subscribers = Intense focus on MMO's and copypasying World Of Warcraft formula for years
Halo (10 million+) = Almost all FPS designed for consoles (to the dismay of pc gamers)
Call Of Duty 4 (12 million+) = All games turning into (mostly) over-scripted throwaway 4 hour SP and multiplayer with RPG leveling system
Diablo 3 (3.5 million in 24 hours - 12 million+ in a year) = Nothing. Fuckall happened.