What a clever idea to put a zipper down the middle of a large quilt to make it easier to handle- ingenious!
I don't know why we use 1/4 " seams on quilts - maybe it has something to do with not having too much 'extra' fabric inside the blocks (all the seam allowances). I was so used to 5/8" with garments that the 1/4 looked miniscule, and as you point out, sure doesn't leave much room for raveling!