Again most of his errors have been of the throwing variety. Remember at one point last year (I believe it was right out of All-Star break), Zim made a few throwing errors and people on here were saying he should move to short and that he would never correct his throwing form!
Practice makes perfect. I'm sure the coaches and even his neighbor Zim are helping Dessie along the way. Sure, it makes you worry a bit, but I think he can improve.