They have no control of the size of the image you post because they don't host the image. You are simply hot linking it from another site. It also has absolutely no effect on their bandwidth or storage because the pic is served up by another server.
Their issue is with the layout of their page and providing exposure to the advertisers.
What I can't understand is why they can't get an IT guy to change the setting so that it automatically adds the width tag to the img html tag. As a web developer that would take about 30 seconds.