If you read up on his history post Hot House it's pretty much the case that he was the main reason ADX was built in the first place. He has his own special cell there that's even more isolated than all the other prisoners.
Silverstein killed a prison warden. That is why he got this extreme form of punishment. And since he is a member of the Aryan Brotherhood, none of the human rights organizations will ever take up his cause. On the other hand, Tsarnaev is already getting a lot of support from various "human rights organizations".
