The big difference is that today's record-breakers seem almost manufactured to be record-breakers. They're the most expensive movies usually, whereas Star Wars was (relatively) low-budget. The Dark Knight and Avatar, while both risky and innovative, still had the full financial support of Hollywood behind them. If you adjust for inflation, Star Wars would cost around $50 million today. If you adjust to 2005 dollars, it would be just a little more than Serenity's $40 million. Has anything in the last eight years with that low of a budget really burned up the box office to Dark Knight / Avengers / Avatar levels??? That first Hunger Games movie comes to mind, but even that had a built-in fanbase from the books.