Epic design chief Cliff Bleszinski has stated before that Gears of War is not likely to hit sales numbers that Call of Duty is likely to. Gears of War 3 executive producer Rod Fergusson agrees with the sentiment, and explained why the ceiling is there.
“I just think Gears has a natural ceiling”, he said. “I don’t know what that ceiling is but people come to Gears of War because we have our chainsaw assault rifle, but I think it also keeps people away in some respects. As many people as there are that come to shoot monsters, I think there’s people that don’t necessarily want a sci-fi experience and having monsters there. I think there are some barriers there but it’s also what makes us unique and what draws people in.”
Source: CVG {link no longer active}
