Thought I would mention that the HD digital releases have been updated within the last week or so. They now include nearly everything available on the Blu Ray release.
After a cursory inspection, the only things missing from the set now are “The Making of Star Wars” and “SP:FX: The Making of the Empire Strikes Back”. I’m not sure why they left those out.
So far the “newer” content is only available through Disney Movies Anywhere and iTunes. Vudu and Google Play, at this point, only have the content that was released back in April.
The concept and production artwork is only available through iTunes Extras.
As far as exclusive content (I’ll post it here since no-one else seems to have ever done it):
Conversations:
Doug Chiang Looks Back
Sounds In Space
The Star Wars that Almost Was
Creating a Universe
The Lost Interviews
The Effects
Discoveries from Inside:
Models & Miniatures
Costumes Revealed
Hologram & Bloopers
Weapons & The First Lightsaber
Matte Paintings Unveiled
The Sounds of Ben Burtt
Other Stuff:
George Lucas On The Digital Revolution (iTunes only)
The Podrace: Theatrical Edit (full 1080p HD)
The Art of Attack of the Clones (DMA only)
The Journey (Parts 1 & 2) (Originally from starwars.com, but here part 1 is a slightly extended edit)
ILM Episode III Siggraph Reel (Originally from starwars.com, and in better quality there!)
Scrap Into Gold: A Conversation with Roger Christian (DMA only)
Dennis Muren: How Walkers Walk (Originally from DC Laserdisc, available free on starwars.com)
1080p Trailers for all six films plus one for the entire saga