I don't really like the fanboyism of James Cameron fans in this forum. But I feel like the people supporting or want AEG to outgross Avatar will pull everything they perceive to be an advantage for Avatar and try to claim that it's run was less impressive than what AEG is achieving, to be biased towards AEG, when they don't do the same for AEG.
They don't consider the time difference between the two releases and the state of each market now and then. You are only pointing to one thing (ER) to say Avatar's perfomance is less than that of AEG, without considering everything else that might point to Avatar's box office run in positive light. I feel like we are not seeing are fair assessment of both movies performances.