It was moved from the center so that the shots line up with the origins of the gun "more naturally." It has nothing to do with play and it makes aiming up for headshots feel like driving a car with a lowered rear suspension.
Fake E: Valhalla also doesn't play better than Sidewinder and Battlecreek did. Bloodgulch was more tongue in cheek because I know everybody hates that level, but if it wasn't fun then it wouldn't be popular. That's the same justification I know you all will give for Halos 2 through 4.