This issue has come to a head with the success of Avatar. By any measure, it's a successful and wildly popular movie, but it's pointless to gauge Avatar's popularity based on box office gross, when the average price paid for a ticket is so much higher than any movie in history. Even box office leaders from 2009 or 2008 did not include huge numbers of IMAX and 3D sales.
The only fair metric to judge a movie's popularity in a historical context is plain 'ol tickets sold. Box Office Mojo has a nice interactive table ranking all-time domestic box office, by dollars, and by tickets sold. By that measure, Avatar, at 76 million tickets sold, is at #26 all-time. Be sure to read the Chart Notes at right- 15 of the 25 movies ahead of Avatar on the list have benefited from multiple theatrical releases- a common practice for blockbusters pre-1980, also Disney movies, and movies by George Lucas and Steven Spielberg.