Apparently this is due to the thickness of the case/lugs. Was told that for the thin lugs, thread on the receiving end of the lug would compromise the structural rigidity hence they went for the spring bars.
Personally I would have preferred the conventional screw-in pin, especially on a delicate case like the PAM532 BUT I'm absolutely digging the thin profile of the case more and more. It's such a joy especially when I'm wearing a sweaters or pullovers...