Sorry, I have to correct you. Locking central differential does not force all wheels to spin at equal speed, rather only the front and rear axles.
To make all four wheels spin at same speed, separate front and rear differential locks are needed which are activated after central diff is locked. With central diff lock engaged only, one front and one rear wheel spinning will cease your forward or backward progress.
The defender has full time 4WD, so that's why it has separate central diff lock, otherwise all part-time 4WD vehicles lock the central diff to transfer power to front wheels.
As far as I know front and rear diff locks are standard only in Merc G Wagen and maybe some models of Jeep. Its an option in TLC series 70, 80, and 105. TLC series 90, 100 and 120 have only rear diff lock option as they have independent front suspension, rather than the solid/live axle in remaining. I think original Hummer also had it.
One can off-course have it fitted as an after market option from companies like ARB etc.