Good point. boxofficemojo.com has this page which allows you to compare the all time list, sorted by inflation adjusted dollars.As you see, GWTW is #1. Hey, The Ten Commandments is #5!
I once saw a breakdown that adjusted for the number of paid viewers, and then ANOTHER one which adjusted for the fact that the population was lower, so they did a conversion for the number of paid viewers divided by the size of the US Population, proving that by all means and measures, GWTW was the most popular movie of all time, by far.