Used to be pretty common with dune buggy type vehicles based on the VW platform to have two hand brake levers. The OEM was a single handbrake lever between the seats pulling wires on both left and right rear wheels so add a second lever and have each lever pullings wires on one side only. Mostly after the success of the VW platform I think the same setup was used a lot in other vehicles but a step on the parking brake setup is harder to modify.
To repeat myself - folks are indeed talking past each other a little bit -- my own experience has been that I never wished I had open differentials, I've been happy with some more sophisticated devices and even with a clutch type posi in front as well as rear I've found clutch type posi to be better on the highway. For a truck full of wet garbage a Detroit Locker has many advantages.
