Stuttering occurs when the speech center of the brain is unable to send the proper signals to the vocal processes (tounge, larynx, vocal cords, hyoid bone), the typical result is the inability to smoothly transition from a beginning consonant to a vowel or complimentary consonant. For example, c-c-car. Because the center for singing is close to the frontal lobe stutterers often have no problems singing whatsoever. Therefore stuttering is a true speech impediment.
Tourette's, however, affects nearly every part of the brain. Many of its victims have not only vocal outbursts but physical ones as well to such a degree that they have to be severely doped up or restrained during bad episodes so as to not harm themselves or others. I suppose that it can impede speech, but that is not always the case and a minor symptom of a much greater problem.
Tourette's isn't just about affected speech but both stem from problems in the brain that can impact speech. I figured that was close enough for this.
Then I also read about an experiment a woman did on a group of orphans in the '50s or '60s where she was hyper-critical of their speech patterns as they learned to speak and thus made every one of them stutter. They recently uncovered the fact that her actions were an intentional experiment and launched a lawsuit. Until that suit came to light she and the man she was working with at the time were seen as heroes in the study of stuttering in psychological circles.
"Jelly-belly gigglin, dancin and a-wigglin, honey that's the way I am!" Janice the Muppet