The geometry of the 4x4 rear end is now - presumably - the same as the standard model, apart from the raised ride height; the Mk 3 4x4 had a fully-independent setup, which worked well but I haven't driven this model far enough to compare with my Mk 4. The independence of the rear wheels on a torsion beam setup is compromised variably, depending on the stiffness of the beam, but then the same is true of an independent setup if it has an anti-roll bar, especially as the 4x4 would need relatively stiff anti-roll measures because of its ride height. I suspect that cost considerations affect design to the extent that many independent systems impose more camber change than a torsion beam.
I'm sure the principal reason is cost; proper coilovers with adjustable spring platforms and damper settings have a lot more engineering in them than the standard setup on something like a Panda. There's also the issue of how you feed the loads from the spring and the damper into the vehicle's structure, as I mentioned in an earlier post. It's conceivable that dividing the loads between separate mounting points could save weight and enable the use of cheaper components such as bushes. Another consideration is the amount of movement experienced by the spring and damper for a given wheel movement; stiff springs deflect by a small amount and you might want the dampers to operate over a greater distance - hence mounting the damper on the suspension arms further away from the pivot point, as they are on the Panda.
