It's a secret key that's part of the decryption process for HD-DVDs. It's not something that would be of interest to most people. But it may be that people are uncomfortable being censored for repeating a "meaningless" string of numbers.
It's true that you can't legitimately play HD-DVDs on linux, but I suspect the motivation for AACS crackers is the challenge of breaking a newer, "tougher" system. Being able to duplicate, rip, and play on linux are merely bonuses.
The people who mandate the use of DRM on HD-DVD/Blu-Ray probably don't even own computers, much less know what linux is.