Originally Posted by Drew Eckhardt

Nope it has nothing to do with "increased stress" after breaking some spokes.

Spokes fail due to fatigue. Since they all had similar average stresses from manufacturing and wheel tension, all saw similar variations from the rider weight unloading them as they pass the ground, and all underwent the same ~750 cycles per mile as the wheels turned round all of the spokes in one group (rear drive side, rear non-drive side, front) will fail about the same time.