To me, an heirloom quilt is made with lace and fancy stitches, like French embroidery. It is usually white or cream and is not meant to be used to keep you warm, only for show. What comes to mind is a quilt made out of someone's wedding dress to be passed down to future generations. An example is a quilt made to commemorate a special occasion, and not meant to be used. IMHO heirloom is a technique not a type of quilt.
Sue