B-b-b-b-ut I d-d-d-d-on't g-g-g-g-et the thread s-s-s-tarter's logic.
(Okay, enough of that).
If there's stuttering in the demo for some people, that just means that they haven't finished fixing it yet. It says nothing about when they will be finished.
As said, if there's still stuttering in HL2, there'll be stuttering in the demo. If they'd fixed it in time for the demo release, they'd probably have released a patch already.