I read an interesting article on sentencing people like this. The theory is that it is symbolic. Sending a message to the victims or the public that this crime was so bad that only a sentence of that length will suffice.
On Ariel Castro, I normally am the one saying, "steady on" to the hang 'em, flog 'em brigade but I can't feel any sympathy. He had a tiny taste of what he put his victims through and hanged himself. Surely that means that faced with it, he realised what he had done. I hope the victims and their families can sleep a bit easier.
I feel a bit like I did when Shipman killed himself. God knows the world does not need this individual in it but I also don't think he should be allowed to take himself out of it and rob the victims of the knowledge that he is suffering a long, preferably dreadful, life in prison.
On the other hand, if the victims feel a sense of relief that he is finally gone, fair play to them. He was the father of Amanda Berry's daughter, of course, and so for her this is another dreadful twist in a life no 6 year old should have been subjected to.