"Avatar" is not the highest-grossing movie of all time

Not even close. The Hollywood statistics are absurd because they do not adjust box-office revenue for inflation. When said adjustment is done, it turns out that the highest-grossing movie of all time (highest-grossing in the U.S., that is) is "Gone with the Wind," followed by "Star Wars" and "The Sound of Music" (see the list of top 100 here). "Avatar" currently sits in no. 14, though it will surely climb as its immediate competition is pretty ancient.