I'm guessing they have a wedge type, but perhaps the wedge itself is not threaded, but instead a nut beneath it. I've also seen a "cone" in place of a wedge, expanding the bottom of the quill tube which is slotted longitudinally.

Aheadsets are awesome, one of the great inventions.

Dahon handleposts like mine, the fork steer tube is threaded *internally*, and the handlepost base has a huge special bolt with 10mm allen, that engages there for preload, and then one bolt (steel base, I think perhaps two bolts on aluminum base) on the side that clamps the handlepost base around the smooth steer tube exterior. It's a good system that works as easily as an Aheadset.