I don't think they have to be killer apps, they just have to stand above and aside from multi-plat titles. Halo 3/Gears of War are both system sellers whilst Killzone 2 and RFOM 1/2 are not because the former are both unique and/or better than the multi-plat titles at the time. Gears of War stands aside from Call of Duty, but Killzone 2/RFOM 1/2 can't get out from under its shadow.
Tease.







