difference between wheel nuts / bolts for alloys and steels on the Jimny?

Most hub centric wheels also have tapered (or spherical) seat nuts/bolts.  The taper resists mechanical precession, which would otherwise tend to loosen the ones on the offside of the car. 

Flat seat nut mounting used to be fairly common on alloys (and only alloys).  The area providing friction is much bigger than on a pressed steel wheel, reducing the chance of unscrewing and, even so, you were supposed to check tightness regularly.  Modern alloys usually have a hard steel insert with the female taper.