The only problem that I see with tearing is if the design is "painted" on. My mom and I ran a custom drapery business for years and we pulled threads on our fabrics to cut them out but when it came from a print we drew lines.
I used to work in a fabric store too and it is a tough call when you cut yardage. If you allow a little extra it is a great thing for the customer but an expense for the store. If every customer gets an extra inch can you image how many inches that adds up to for a place like Joann's? Sure the store can eat the expense but then they have to add it on to to their prices to make up for it.
Tough dilemma.