It's not the length of the spokes that matters (the difference is marginal) - it's the angle they make - the further off radial they are, the stiffer the wheel is in torsion. That's why track bikes have high flange hubs. In theory, this is most important on the drive side since that's where the torque is being applied, so I guess Campy were trying to save weight by removing material on the non-drive side while keeping the drive side torsionally stiff. I don't know how much difference it makes in practice - if the hub body is really beefy it should be able to transmit the torque to the non-drive side too. You do see some road bike wheels laced up tangentially on the drive side and radially on the non-drive side.
It's not the length of the spokes that matters (the difference is marginal) - it's the angle they make - the further off radial they are, the stiffer the wheel is in torsion. That's why track bikes have high flange hubs. In theory, this is most important on the drive side since that's where the torque is being applied, so I guess Campy were trying to save weight by removing material on the non-drive side while keeping the drive side torsionally stiff. I don't know how much difference it makes in practice - if the hub body is really beefy it should be able to transmit the torque to the non-drive side too. You do see some road bike wheels laced up tangentially on the drive side and radially on the non-drive side.