The 2004 release seemed to be building up to the release of Revenge of the Sith. Some of the changes, like Palpatine in ESB and Anakin in ROTJ show that they intentionally took some cues from ROTS, which was pretty far along in production at this point. They waited until 2006 to release the OOT on DVD, after the Saga had already been completed. The 2011 release seemed a bit out of place, as there was no big landmarks surrounding it. Then again, the ST was not even a realistic idea at this point in time, so you can't blame them. Then a few years later, the combo packs are released, which actually bring back DVDs. Pretty weird; you'd think it'd be the other way around. Though in general, Lucasfilm generally takes its time when bringing Star Wars to the newest home video formats. Sometimes it works to build interest, sometimes, it just feels overdue.