If you remember Dark Knight, Avatar and Avengers, the first weekends were basically all sold out completely.
100 million is still an amazing opening and I could see the overall gross throughout its run be pretty high.
Edit: Box Office Mojo predicts 137 million opening.
http://www.boxoffice.com/featured_st...pected-journey
This site says around 80 mil
http://www.comingsoon.net/news/weeke...s.php?id=96680
So you subtract a bit for the lackluster reviews that weren't out yet when that was published and my estimate might not be that far off.