I always use batting and a backing - I used to mainly pillowcase but now usually don't use that method anymore - just my personal preference. The one time I didn't se a batting and backing I regretted it cuz if you wash it (which I usually do at least once before putting it away for the season), oh the wrinkles and threads coming out of the woodwork to say hi - cut me!!
I've been tempted to do the 10 minute table runner but am thinking of buying the thinnest flannel I can find to put in it cuz I just think it would hold better with at least some batting.
Also, if you decide to put a backing on, I agree 40" is too big of an area not to at least put a few quilting lines in.