Why did the major 1st parties and 3rd party publishers wanted to pull out of E3. I hear the main reason was that they wanted to "control the message". Take Sony and EA's showing at E3. They were largely considered "lackluster" by the press for their titles and especially what Sony had to show for the PS3.
I don't take those things too seriously. Anyone who recalls how badly Halo showed in 2001 will realize that things still come together at the end for many projects out there (albeit with lots of wasted effort and overtime).
However many people in the press and therefore the consumers do take these things seriously. Sony tried, with their "10% completed" stickers on their kiosks, but people pay attention to what is on the screen and with the Sony representatives vastly outnumbered they couldn't explain in detail the caveats of what was actually running.
Now if all projects had Agile releases and focused on consumer value first it would be a different show. :)
One of the things we learned from the doing Sprint reviews is that the amount of hand-waving and "description of what you are about to see" before we saw the game running is inversely proportional to the consumer value of what was produced during the Sprint.
Maybe this scales. Maybe the change of formats for E3 is an opportunity for marketing to do more hand waving.