sounds like you know about most of that stuff anyway. I think that the person who made that wiki was thinking along the lines that a 100 lb.ft engine will exert the same strain on the differential in the same gear regardless if it is producing that torque at 2000rpm or 8000rpm.

its the torque that the driveshaft is transferring that is what matters, how fast it is spinning is irrelevant. Perhaps they should have narrowed it down to that rather than engine torque