I've not had any problem with threadless headsets ( at least in regard to the threadless design ), and nor has anyone I know.
( I have had headset bearings fail, but that's not an issue of threaded vs threadless. )
What problem is concerning you?
The stem clamp system works just fine.
The star nut is just used for the initial pre-load to remove any play from the system, and then the stem clamp holds it all in place. It's possible to actually remove the cap-bolt totally after the stem is clamped.