The power divider is necessary also because it is almost impossible to have tires with the exact same rolling diameter. The power divider compensates for slight differences in tire diameter in a similar manner to an automotive differential compensating for differing distances traveled by a car turning a corner. If one wheel on each axle has no traction, even with the power divider locked in, the truck will not move.
Some of the newer BIG trucks have the standard power divider as well as a differential lock, which locks the differentials side to side. All power is divided equally between all four drive hubs.
Crabbyappleton, I have found that the rear drive tires on a semi tractor wear faster than the front axle drive tires. I am not sure if that is due to the rear axle tires scuffing in a turn or if the design of the power divider unintentionally allows more power to get to the back axle.
