The directions of rotation of the propellers were the result of a considerable amount of Wind Tunnel testing. In the "standard" configuration (all the same way) there were 2 contradictory problems with aerodynamics and internal noise. These meant a radical approach was needed.
This arrangement means that neither outboard engine is more critical than the other in the enigine failure case - both are more like a Herc #4 than a #1. Each wing reflecting the other then produces a symmetrical flow across the wing and, as importantly, across the rear fuselage and VTP. There being no critical failure side means a smaller VTP = weight saving. As a bonus the paratroops will also get a smoother ride. With this arrangement the troops will be steered away from the aircraft on exit. Neither side will be thrown under the aircraft to wrap themselves around their mates from the other door.
From the noise perspective - the main noise sensed inside the aircraft comes off the blade tips. The outboard noise becomes almost irrelevant whilst the inboard noise continues to follow the direction of rotation and tries to "enter" the aircraft from underneath - there is thus a far greater noise absorption (attenuation) because of the cargo bay floor.
There you have it - DBE benefits for all.
