If I'm not mistaken, it's to compensate for the camber of the road.
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Yes it's the wrong way to compensate for road camber, the driver's side is set higher to compensate for the (assumed) usual sole occupancy, as well as the extra weight involved in the controls.
My 76 RRC also had different length left and right front springs for driver weight compensation.
Yes. Most Landrovers have had different L/R springs. This is almost inevitable if you want to have long travel suspension with no or weak sway bars, and want the vehicle to sit level at normal load.
Most cars have so little suspension travel and/or strong sway bars as to make this unnecessary, as they are optimised for handling on road rather than offroad.
Series Landrovers had their empty weight concentrated on the driver's side (especially RHD) with the driver, fuel tank, battery transfer case, steering gear, pedal gear (and on some the spare) on that side. The engine/gearbox/radiator is offset the other way, but it is not far off centre.
I did a mechanic apprenticeship at a Mazda dealer in 1979 onwards and worked in a couple of Toyota dealerships before I left that trade, it was a standard thing on everything from a little Mazda 800, corolla etc upwards, the driver's side spring was set a little taller than the passenger side. Don't know if this is still the case, I'm out of date there like everywhere else.