Modern DRM schemes like AACS 
  employ methods to change keys 
  for new works. So when crackers 
  find a key that allows them to 
  circumvent the DRM scheme they 
  can't publish it or it would 
  soon get useless and they would 
  have to do the work to extract 
  a key again. 

Who would EVER care about a cipher key, when YOU STILL NEED TO EXPOSE THE RAW PIXEL RASTER, AND AUDIO CHANNELS TO THE END USER, IN ORDER FOR ANYTHING TO BE VALUABLE AT ALL?

Users will always eventually get the whole thing in the clear, in straight-up plain text somehow, eventually anyway. And all anyone needs is a buffer big enough to capture it, and it's trivial to assemble one.

You need to be able to watch a movie with the naked eye, and hear the sound with your ears. That's how movies work.

It's trivial to capture the raw data, and people have been living with NTSC quality picture and sound for decades.

This is not about perfectly matching the SHA256 hashes of the original MPEG artifacts. People just want a copy, and it's easy to skim one, somehow, one way (cracking) or another (brute force direct copies of the image frames and pulse code samples, at the signal source).