The other kind are just for show-off purposes. It's much easier for someone to grasp what a cover will look like on a shelf when displayed like this:
versus this (which is the image you would print, cut out, and put in a case yourself):
Also, keep in mind that the standard size for a printable DVD cover is:
3240x2175 pixels at 300 dpi
Spine width = 170 pixels, centered