Megatron's bio from the movie based toy whose images are posted on TF08.net:
"Trapped in the black, crushing depths of the sea, his mind inert in the grip of stasis lock, Megatron knew nothing of the desperate search mounted for his remains by the other Decepticons. When he was finally brought back online, their effort and sacrifice meant little to him. The only thing that had any meaning was revenge. He would have his vengeance against the human boy who cheated him of his prize, and he swore to celebrate over the smoking wreck of Optimus Prime".
Flashbacks huh, unless this entire movie is a flashback then the above news would be false. But since we all know better then that, one can only conclude Michael Bay was leading the fans astray as he was planting a nice surprise for Megatron's fan's. Really though, who out there believed that Megatron would not be in ROTF. That's like having salt with no pepper, or cookies without milk. It just didn't make a lot of sense.