The right side is blank on some pages because it is occupied by things on other pages. For example, if you click on a tree mail, you will see all of your tree mail options on the right, and the page is rather short (if there is 1-2 messages for that tree mail). You will see, even at the top of this page, there are 2 options for thread management, but the thread is long, so the rest of the page will be blank (or there will be an ad).
