well from my limited understanding.. the open diffrential act to supply the same amount of torque to both wheel every time.. when traction on 2 wheels are diff and the amount of torque is same on both wheel , the one with less traction will start to slip.. its like pushing 2 block of stone, one on cement and the other one on ice. if u apply the same amount of force, the one on ice will be faster loh.. its not easy to understand i presume..
in clutch type LSD however, both wheel are always "trying" to match speed, when traction are different on both wheel, the one with less traction will start to slip, the clutch on the other side of wheel (with more traction) will spin at identical speed, the amount of force/grip of the clutch to withstand from spinning is the same amount of power transffered to the wheel with more traction loh..
I'm no sifu.. just sharing something i found on net oni..