Why do images of DVD covers include the spine?

[minor muppetz]

Back in the VHS era, whenever an image of a video cover was shown in advertisements (whether print or televised), we'd only see the cover. Flash-forward to the DVD era, and whenever a cover is shown, the spine of the DVD is shown as well. Anybody have any idea why the spine is always shown in these images? Does the packaging make it difficult for the cover to face straight torwards the camera?

 

[Sgt Floyd]

I've always thought it was to make it look more like you were looking at the actual dvd instead of looking at a flat "poster" :/