This post was published more than a few years ago (on 2005-07-01) and may contain inaccurate technical information, outmoded thoughts, or cringe takes. Proceed at your own risk.
Not sure why, but the page for the HD version of the Serenity trailer has disappeared, although the standard size trailers are still there. I notice, though, if you click the "Trailers" link on the main movie page, there is a "High Definition option under Windows Media, and now QuickTime. What gives?
You can still get it here (for now): http://www.apple.com/au/quicktime/hdgallery/serenity.html