I worked with some guys that wrote some of the first DVD authoring software and this is what I understood from our conversations.
Burning a DVD data disk is no more difficult than a CD. But you don't just write files on the disk either... it has to be a certain format. Just like CDs have a certain format.
Burning a DVD video disk is another matter... it's very difficult to interleave all that stuff in a way that lets a DVD play smoothly without interruption.
