theres way more stress (and different forces) put on the threads of a starnut/fork than there is on a clamp.
There should be almost NO stress on the starnut or the threads once you tighten down your clamp. Give me a break.
As a matter of fact, once you use the bolt and starnut to set your headset adjustment, you could tighten the clamp and remove the bolt from the starnut. If you have a good clamp, it should be doing ALL the holding once it is tight, since it is clamping the outside of the fork steer tube.
On a threaded fork, the upper race and the lock nut do the job of setting the headset adjustment.
On a threadless system, the bolt/top cap/starnut are used to set the headset bearing adjustment by pulling the clamp, or the bars down against the upper race to set your headset bearing adjustment. Then you lock that adjustment in place with the clamp.
I like what James did with the Scorcher too. By putting in that lip, the starnut can't slip. I just figured we would make ours with the threads built in so you wouldn't have the hassle of pounding in the starnut in the first place.