Physiological factors can, and do, contribute to development. In my opinion stuttering is a developmental issue. Speech is a learned process/skill. It's quite complex. Auditory feedback definitely plays a part in speech. As do physiological factors. But the stutter itself is not physiological. We see peaks and valleys with regards to disfluency. We see the stutter develop. We see effective therapy that allows the PWS to achieve fluency. If stuttering were physiological, I'd be hard pressed to understand how speech therapy could help achieve fluency. Physiological factors contribute to developmental problems. Stuttering is not a physiological problem.