It really isn't fair to compare two different eras. In the 30s, 40s and 50s, there was really no competition for movies other than radio. Today, there are hundreds of ways to spend your entertainment dollar, so yes, less people are going to the movie theaters, but with ticket prices increasing, revenue is at a record high. With an actual IMAX screen or IMAX experience costing up to $20 a ticket, millions are willing to pay.
In addition, many more movies are doing well overseas and with ancillary revenue, movies do fine.
Yes, but it still has to be adjusted for inflation, and nothing comes close to Gone with the Wind. Which is even a better result considering there was half as many people, and most people had far less discretionary spending available.