It's definitely a little frustrating considering that Apple is 100% capable of getting this out sooner or broadcasting it live. (plus, I'm sure some news network would love the rights to live broadcast the event.)
Yea, this used to bother me too. I thought it was just laziness on their part.
Actually, when you figure they're going to render out the slideshows & animations that were projected live on the big screen, composite those in to the vid, choose from different cameras to keep it dynamic, & encode the qt video, 6-8 hrs starts to make some sense.