I think that initially when I heard that some people entered shows with quilts that others quilted, I also thought like the OP...but then I realized that you are supposed to give credit to the one who actually quilted the quilt if it was a different person than the piecer. So, if that is the case, then both are given credit and that seems fair enough.
The only reason it seems wrong to many is that if the judging is the "quilting" primarily (as opposed to the piecing of the top), then it seems like the wrong person is getting the ribbon. However, it appears like the judges have figured it all out and seem to cover all the bases, making sure everyone gets the credit they deserve.