Compression has something to do with it, but a large part of it comes from having a lot of Ku capacity driven at relatively high levels. Ka capacity doesn't yield quite as well as Ku capacity as it requires more error correction.How is Dish able to continually add more and more HD each month without any more birds being launched?
Dish is also using a different encoding scheme that seems to yield better as well.
Another big win comes from transitioning to MPEG4 on the Eastern Arc.