Well, a surprise also would have made it worthwhile.
Marvel was giving its presentation and it was the end and they were wrapping up when Sam Jackson came out.
The real Sam Jackson. There are no substitutes. P.S. He apparently is working on a comic book. No complaints about him, it's not only well established that he's a comic book fan (so he's actually wanting to make comic books, not just slap his name on something), but do YOU want to be the one to tell Sam Jackson he can't do something?
Jackson is onstage and starts revealing the cast of the Avengers movie. So here's what we got:
Chris Hemsworth as Thor
Chris Evans as Captain America
Scarlett Johannsen (presumably Black Widow)
Robert Downey Jr. as Tony Stark/Iron Man (who also introduced some of the cast)
Jeremy Renner as Hawkeye
Mark Ruffalo as Bruce Banner