Is Marvel jumping the gun by putting The Avengers into production months before Thor and Cap come out? They will have no choice but to release the movie at that point, but it could be at a significant loss if too few people show interest in Thor and Captain America.
That's the risk. I think if those two films don't do well Avengers will be very Iron Man heavy in promotion, maybe even made to look like a de facto IM3. That's the only back up plan I can foresee, make it look very IM heavy. Can you imagine being in the meeting room during production of Avengers if the news came out that Thor did poorly at the box office? I'd love to be a fly on the wall during that meeting.