I think the requirement of hand binding is the fact that, if done correctly, the stitching is invisible on the back side of the binding, i.e., the stitching is executed well enough that you don't see it when looking at the back side of the quilt. I agree that machine quilting the binding is more and more acceptable and can be done very nicely, but the point at least with show quilts is to not see any binding stitches.
Christine
Cedar Valley Quilts
www.cedarvalleyquilts.com