It's called Field of Fire (FOF). Turrets are placed along strategic points of the ship's hull for maximum effectiveness and for the best cover. So little turrets over such a large area? Try a half a dozen flak guns and about that many AAA beams on one side of an Orion destroyer.
And by the way, destroyers and juggernauts (it's spelled juggernaut, not juggernaught) have damn good fighter cover and ship to ship power. Why do I say this? I play this game on Hard and Insane, depending on what I feel like playing, without cheats, and it's freaking hard to get close without getting hit by AAAs.