Quilting prevents fabric shrinkage. Unshrunk fabric that is closely quilted will not shrink in the same way that unquilted fabric shrinks in the wash. That is one reason why I don't bother to pre-wash fabric for shrinkage. Plus, I like the old-fashioned look of 100% cotton batting; the fabrics and batting shrink up together about 3% (amount of shrinkage is controlled by the batting, not the fabric -- as long as the quilting is reasonably close together).
I should add that people who like the flatter, more modern look for quilts do probably have to pre-wash fabric and use a primarily poly batting to get that look. It's a look I often prefer for wallhangings.