I think expecting/wanting "extra" to make up for possible shrinkage is about as reasonable as expecting extra meat to make up for the bone or fat that is inedible.
The store probably pays for the fabric as it comes on the bolt. So if there are 10 actual yards on the bolt, they were probably charged for 10 yards - regardless of how it is on the bolt.
That said, I will favor a shop or store that cuts generously to one that cuts "short."