There's an article about the box set it the newest issue of the Star Wars Fan Club magazine. The claim is that Lucas and Spielberg didn't have the time they really wanted to be able to devote to the project until recently. There's also some previews of what'll be included.

Now if we could just get him to see reason about putting the original AND special edition star wars releases onto DVD. You'd think the simplest reason would be - if he doesn't someone WILL, in a pirate version, because the demand is out there. So why shouldn't he do it and get all the credit?