You want to know why? One word: ONLINE

This is all personally my opinion but it's pretty substantial and reasonable:

HD movies will eventually be released online over online distribution networks as downloads. Disks will no longer be used as a medium. Eventually there will be a new medium (tapes to disk to harddrives to ?) Disks will eventually be replaced, they take up space, scratch, and have to use equipment to read them. Other alternatives will eventually take over.

-HD movies are already being streamed or downloaded online and will continue to evolve and grow
-Music and video services such as ITunes are already allowing consumers to directly pay and download movies over the net
-HD movies provided by Cable TV providers such as DirectTV go directly to a harddrive or stored temporarily
-HD movies are already being recorded by camcorders capable of storing video to harddrives and not discs
-As higher (and smaller) memory formats are developed capable beyond the limit of bluray and hd-dvd memory capability, bluray and the disks they use will become phased out

Don't take this following example as being equal to the HD-DVD and bluray situation! It does however represent one present example of the disk format failing...

-UMD's on the PSP failed because they were too expensive and you could just download the videos off the net and put them on memory sticks. The UMD disks weren't needed.

Heck, the movie industry is already on such a slide with such terrible films coming out that I'm not even sure if people are interested in movies. I haven't been to a movie theater in like two months. I've downloaded (legally) the majority of the movies I've seen in the past year.

**READ BEFORE POSTING**
Blu-ray and HD-DVD's memory will serve well for GAMES. Soon enough though, games will begin to run off other forms of medium as witnessed by XBLA or even the Virtual Console. So all you people fighting over which format is going to win or what not, you're window of opportunity is limited because the transition is already in motion and don't get pissed when you've purchased a HD disk player to find it useless in a couple years.