Highest grossing of all time is such a BS number when not adjusted for inflation. Movie prices have risen so drastically that it takes many fewer people to see a movie these days to rank it highly compared to past years. For Avatar this is further exaggerated by the fact that they charge even more money to attend an IMAX film.
I prefer to look at the inflation adjusted list, which measures by tickets sold. Unfortunately this list only shows data for the US and Canada, but it's very telling-
http://en.wikipedia.org/wiki/List_of_highest-grossing_films_in_the_United_States_and_Canada. From that list, you can see that only 2 movies in the last 30 years make the top 10 (Star Wars misses the cut by 3 years), and you have to drop to 27 before you find a movie from the last decade (Dark Knight).
There are many reasons for these drastic differences and I accept all of the arguments, I just find it a bit ridiculous that we get so hung up on nominal dollars for ranking movies without taking into account that ticket prices have been jacked up to ridiculous levels over the years.