true. The arguement could definitely be made that keeping a dying man in prison away from doctors, constant medical attention whenever needed, and his family and such is a textbook case of "cruel and unusual punishment", which isn't allowed.
Death Penalty is also "cruel and unusual punishment" as the constitution states is prohibited. The U.S is about the only nation in the western world who practice capital punishment, no countries who do will be admitted into the E.U. In fact very few countries world wide practice it anymore. Hence "unusual".
The psychological torture sitting behind bars knowing exactly when you will die as well as the extremely painful accidents that happen when the execution process goes wrong, is what I would consider pretty cruel.
Extremely simplified argument, but yeah.