The fact Deadpool test footage leaked before this makes me sad. Not that I'm complaining about the Deadpool footage, but never even expected to see it.
I find it impossible that no one recorded the footage with the intention of putting it online. Unless security was the strictest they've ever been during the panel.
A guy on YouTube says he had it and uploaded the Scarlett interview that happened right before the trailer was shown. So it's out there, just gotta be posted.
I think the difference between this footage leaking and Batman V. Superman is that Warner Brothers probably wanted their footage to leak and build hype out of curiosity. Marvel doesn't need more hype and likely doesn't want anything to leak. However, several 15 second videos were leaked last year of their upcoming movies, so we will probably see some footage at some point.
It is true that DC and WB probably let it get out there because they need as much positive press as possible, but wouldn't a logical thing to do afterwards is to release the footage in HD and go "Well, it's been leaked already, so there's no reason not to release it."? Sure, Marvel doesn't necessarily need to save face unlike WB, but I always figured that Marvel would release the footage just for the massive amount of people so upset that we won't get to see it, to quote Joss, "For a while". IIRC, the original Comic Con reveal teaser for Age of Ultron came out a couple of months after it was originally shown, so it would be absolute torment to have nothing until fall. EDIT: On a different note, that cover of the Pinocchio "I've Got No Strings" song really gave me the chills. I guess there's gonna be some parallels between him and Ultron, or maybe he'll make that analogy himself in the movie, and it's not exclusive to the trailer. Either way, it's awesome.
Robert Downey Jr. Teases How Hulk Vs Hulkbuster Battle Ensues In AVENGERS: AGE OF ULTRON SDCC '14: Take A Closer Look At The HULKBUSTER Fist From AVENGERS: AGE OF ULTRON
I wonder if this teaser trailer is going to be the end credits scene for Guardians of the Galaxy After all we did get an Avengers teaser after Captain America the first avenger. Also the music it is a really slow (different) singer version of the song from Disney's Pinnochio "I've got no strings on me"
James Gunn said the AoU Comic-con footage would not be at the end of the credits. http://www.comicbookmovie.com/guardians_of_the_galaxy/news/?a=104600