Hm, not really true re: center diff.
Unless there's been some mix-up, the center diff in the T3 is a torque biasing differential. The F&R being open, there's a very good reason you'd want to potentially lock the rear. Torque biasing requires torque potential on one side to transfer any to the other.
So take the scenario of a ditch, if you fully lift one front and one rear tire into the air, you can't make any torque to either tire on the ground. You're stuck, because you have an open diff on each end, and a free spinning wheel on that open diff.
If you can lock the rear, you will make torque at the rear wheel that's on the ground. You'll still spin the free wheel in the front, but you at least have potential for movement in the rear.
There's a whole mix of differential setups for different scenarios, honestly just a limited slip unit in the rear would prevent a lot of common ones.