I've seen tested this same argument.
The majority of diff movement was recorded as pretty much straight up and down over road surfaces, and the fore and aft twisting of braking and acceleration.
This is why they mount shocks near to vertical and on opposing sides of the housing eg. one at the front of the housing and one behind.
They just want to cover what the suspension forces will be 90% of the time under normal driving conditions.
This is for a road driven vehicle, 4WD's differ only because of their intended useage. But you will still find even extreme off road desert racers and monster truck that still run the shocks pretty much vertical.
High horsepower will benefit from the shocks being as a pair at the rear of the axle on a 4 link set up or one front/rear of a leaf sprung rear to combat spring wind-up.
In the end, it's not too much effort to chop and change and see what works best.
