Here's a pretty interesting story about why Apple.com, of all places, hosts movie trailers. It all goes back to that first Star Wars: The Phantom Menace trailer back around 1998 (which I watched hundreds of times, before I saw the actual, less exciting movie).
Over on Quora, a former Apple employee named Chad Little says that "Lucasfilm had posted a rather crappy trailer on their site, and the team at Apple was appalled." So Apple allegedly went back and looked up DNS records to contact the Lucas team, and it had the movie encoded with QuickTime rather than the RealVideo that was being used. At the time, Apple hosted the trailer with a little company called Akamai, which has since grown into one of the world's biggest providers of web hosting.
The deal worked so well that Apple ended up hosting other movie trailers, and in recent years those trailers have served as great demos for iTunes and the Apple TV service as well. Little claims that Apple doesn't actually pay for content rights, but movie companies get to share their trailers in a common space, and Apple gets great branding and display content for its QuickTime video specs.