Just seems to me that it's way too soon to be thinking post-credits for IM3. Also doubt that they would be tinkering with "The Avengers" at this late date. That's why I'm guessing that it's the post-credit scene for "Avengers." Maybe they waited for all the guys to be in town to shoot it. Much easier to schedule that way.
Of course, I could be miles off base with my theory.
Wow don't you think it's crazy that they put a new scene this far in the game? Because it is going to be launched in less than three weeks, it is going to be in every cinema of the world in just 2 weeks, I found it risky to do that but well better for us fans right?