In the above example the width of the three elements stays within a certain range. Most of the times stacking is easier to do with an even number of elements, it keeps the layout more balanced. However, there are variations that can create slightly different effects.
In this case the single element (number 3) could have been centered for example. Stretching the element across the full width of the page is another possibility. Both variations are displayed below.
(As do these paragraphs...)