torn fabric also weakens the fabric around it, so whether or not i'm paying for it i prefer cut. considering the price per yard these days, an extra few inches doesn't make that big a difference in my total price.
btw, as you said, they all tear crooked anyway, and most stores wont give you extra inches for free, sometimes as many as 6, to compensate for that crookedness. 3 " on one end and 3" on the other adds up.