SJD,
My guess is that maybe the HD version is the one that is divided into sections or segments. I was not really a big fan of the SWA Sonar X2 Mix Clinic, but it is divided up into smaller sections. For me it makes going through the course much easier.
For example, If I can't remember a certain thing that was said about working with the video or the step sequencer, instead of calling up the 9 hour video and scrolling half way through it, I just click on the segment and watch it from there.
While I have been going through this series that Karl put together, I am starting to become convinced that his video is the most informative one out there. There is a lot of information to digest. Karl knows his stuff!