There is a rumor that Marvel Online isn't coming out, based off an interview with Cryptic where they said "Cryptic Studios collaboration, Marvel Universe Online, has hit
serious, potentially stalling, development troubles." It kinda makes sense because we just reported a few days ago about City of Heroes getting purchased and slated for major reinvestment. Cryptic has been talking about their other projects exclusively and trying to divert attention away from the Marvel Universe game.
The MMO market clearly has a space for a game based on superheroes, but probably not more than one. My bet would be that Marvel hit some snags when they realize exactly how much investment money and time are required to compete in the MMO field. It is possible they put the game on a much longer development timeline and just didn't want to announce it was coming out in 2010. Is that really very different from simply saying it's cancelled anyway? For now it's basically the same to all of us.