Microsoft is already bloated with late 2010, Gears of War 3 now would force people to actually not be able to choose one game over another with so many great games slated for that period already. Best they save Gears of War 3 for the middle or even end of next year, I think.
Epic is probably going to be releasing multiple games, remember how they keep saying they have multiple projects they never announced yet? I would be shocked if Microsoft did not have at least one more exclusive from them planned, too. Gears is too big of an IP now to just throw up against with one of their other big IPs. By actually waiting longer, sales could be better for both games. [/teaching shadi how the industry works]