I've seen that. However, in ASMI's presentation to Little League Baseball in which they advocate for the pitch count rules, you can see through out the presentation, the speakers say that youth pitchers should not throw a curve ball. However, when they present their studies, they sort of stutter, hem and haw and say that there really is no evidence that throwing the curve ball is more stressful on the arm. It is almost like they are wanting to stick to the old addage that a curve ball is bad, but they can't prove it. Here is a link to the presentation:
www.littleleague.org/pitchcount/pitchpresentation.htm
They talk about doing a biomechanical study on the forces placed on the arm while throwing a fastball, changeup and a curveball. The study specifically shows that fastball is the hardest on the arm, curveball is second and changeup is easiest.