What will I do after Indy 4?
Why, I'm going to run out to Wal-Mart and buy ALL the "Official" Indy 4 merchandise I can get my hands on.
I will just HAVE to have the Official plastic fedora, the Official plastic jacket and the Official plastic carry bag, not to mention the Official Indy Whip (plastic, of course).
If you haven't noticed, movies today are all about marketing; which George Lucas is becoming a master at. Every new movie coming out, especially the Star Wars movies, has toy and clothing tie-ins; Batman Begins, Star Wars, Fantastic Four. It works either of two ways: you see the action figures weeks before the movie releases, buy it and go see the movie; or, wait to see the movie and then run out and buy all the cool stuff you just got through seeing.
It is a way to prolong the experience.