[untog]

and every few years there is a new "biggest grossing film of all time."

That, at least, can be accounted for by inflation: http://boxofficemojo.com/alltime/adjusted.htm

Titanic (1997) is the most recent in the top ten (at #6). Avatar is the most recent at #14, and one of only two movies from the 2000s in the top 30. Movie revenue is dropping. Roger Ebert has a rundown of why 2011 was such a terrible year:

http://rogerebert.suntimes.com/apps/pbcs.dll/article?AID=/20...

As for TV- no, it isn't in such a decline. But more and more people are watching online, and the existing TV networks don't have the stranglehold on content that they do on cable/etc. A lot of people watch stuff on YouTube, Netflix is making original content... there is space to disrupt TV watching yet.

[archangel_one]

Probably worth noting that the inflation-adjusted list, while more accurate than a non-adjusted one, is only the American domestic gross. It's quite plausible that the international gross would look different - one might expect that the trend there for Gone With The Wind would look a bit different to Avatar.