Why do people continue to call games the -killer? For example... multiple games have been hyped as a Halo Killer. Halo can't be killed. It is a title that exists and has been successful (wildly successful). No game will ever change that hence no game will ever kill it.
If GT5 and Forza 3 launched within a week of each other and droves of potential customers dropped GT5 and instead bought Forza 3 then you have a "killer". Other than that scenario, a sucessful game can't be killed unless the conqueror somehow makes the conquered sell negative numbers and go back to zero.
In short, drop the "killer" shit. It's old.