Most of the press believes that the reason MS supported HD DVD was only to prolong the format war while they organized their own format of DD. While HD DVD and Blu-ray were busy duking it out, MS would be quietly building their DD library.
Edit @DarkVader:
They did not plan on the war ending so soon as once Warner Brothers went Blu-ray then HD-DVD was done, but it did not blow up in their face as MS did build up quite an impressive update with their movies. Before E3 2007 the movie list was horrid with only a few movies that you might have heard of but then once E3 2007 rolled around they announced a partnership with Disney/ABC to have their Movies/TV shows available for download. After that, movie and tv studios began pouring into Xbox 360 and now almost every major TV Studio now has content on Xbox 360 including FOX, NBC, ABC, and CBS and a lot of Movie Studios also showing their support. By the time Blu-ray had finally matured with the format war in the distance MS drastically increased their video store into what it is now, and it's only going to get bigger with the addition of Netflix.
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