Ron, it's not that easy.
The world has changed so much, and so many more entertainments are available now than when, say,
Gone With The Wind, The Sound of Music, Ben Hur and even
Jurassic Park were released, that bums on seats is no longer relevant. For these movies (well excepting
Jurassic Park), there was really only one way to see them. Go and put your bum on the seat. That's why GWTW was rereleased something like 31 times before it turned up on televsion.
For example, people can now go to the theatre, or wait 6 months for a DVD release, 12 months to get it on Foxtel BoxOffice, or another year and then watch it on free to air television, instead of forking out cash to see it at a theatre. Or even download it from an internet stream, make copies, and distribute them within days of release.
Do you know what the most Downloaded movie of all time is? you guessed right -
AvatarBack in the 1950's, I used to go to the (unlamented) Belmont Pix every Saturday afternoon, regardless of what was on. It's just something we did, because there was not a whole lot else to do. Now there is, and this sort of thing does not happen anymore.
Much of the world is also in recession, so it also shows that this entertainment is attractive enough for masses of people to use limited discretionary expenditure and still put thir bum on a seat.
So, I will produce three lists, none of which are definitive, all very different, and I must say, I have only scratched the surface of what is a very complex and difficult issue to discuss in such a brief

post.
List the First. Top Ten Grossing Movies of all time (World)
1 Avatar 2009
2 Titanic 1997
3 The Lord of the Rings: The Return of the King 2003
4 Pirates of the Caribbean: Dead Man's Chest 2006
5 The Dark Knight 2008
6 Harry Potter and the Sorcerer's Stone 2001
7 Pirates of the Caribbean: At World's End 2007
8 Harry Potter and the Order of the Phoenix 2007
9 Harry Potter and the Half-Blood Prince WB 2009
10 The Lord of the Rings: The Two Towers 2002
List the Second Top Ten Grossing Movies of all time (USA only)
1 Avatar 2009
2 Titanic 1997
3 The Dark Knight 2008
4 Star Wars 1977
5 Shrek 2 2004
6 E.T.: The Extra-Terrestrial
7 Star Wars: Episode I - The Phantom Menace 1999
8 Pirates of the Caribbean: Dead Man's Chest 2006
9 Spider-Man 2002
10 Transformers: Revenge of the Fallen 2009
The only other "meaningful" list (world box office attendance is simply not available for reasons I will go into in another post if you wish) is an inflation adjusted list (USA only), i.e., a guestimate of "bums on seats" based on the cost of tickets over the years and is very different to the above:
1 Gone with the Wind 1939
2 Star Wars 1977
3 The Sound of Music 1965
4 E.T.: The Extra-Terrestrial1982
5 The Ten Commandments 1956
6 Titanic 1997
7 Jaws 1975
8 Doctor Zhivago 1965
9 The Exorcist 1973
10 Snow White and the Seven Dwarfs 1937
(
Avatar is currently at No. 21, and will probably finish at No. 15 or 16, which is pretty impressive, considering we are talking about 20,000+ films released since the first MAJOR sound movie -
The Jazz Singer. World wide it will be much higher, as over 70% of the revenue
Avatar has earned is overseas, compared to a lower 55-60% for most releases. it will finish up in the notional top ten)
Note the age of most of these movies on the adjusted for inflation list. It was a different time, and people went to the pictures far more often, but again this list is questionable for quite a number of reasons, and
The Sound of Music may actually be the Number One bums on seats movie for international releases (and I do not even want to investigate Bollywood, the number of movies only released locally in India and the thousands of millions of tickets sold to indian audiences, as I suspect some of them would sink even
Titanic)
ETA: I had a longer and much more detailed post

on this subject nearly completed and the usual "crash, tinkle, data gone" occured. I will answer any specific questions from this post in (long and boring) detail
Norm