Movieweb gives us the info:
The Avengers is currently filming in New Mexico, and because of this, studio leaders at both Marvel and Walt Disney Pictures decided that they weren’t equipped to meet fan expectations at this point. It was deemed detrimental to promote the film, and too costly to shut down production for a week…Walt Disney Pictures, who is producing The Avengers with Marvel Studios, is withholding its upcoming slate, which includes both John Carter and Lone Ranger.
It is a big blow, seeing how WB is also going to be AWOL and thus no Dark Knight Rises or Man Of Steel presentations of any kind (although that might rule out viral, off-campus publicty gags, like the 2008 SDCC with The Joker ‘gang’) but this means more room for Sony and thier Marvel properties: Spider-Man, Ghost Rider and MiB sequels and reboots. Plus whatever Fox and Lionsgate have. Still, with major C2F projects taking a backseat, it really speaks volumes.