Heh. Unfortunately it is more complicated than that. I think the line includes cruelty along with the 'and' to attempt to put some sort of limits on punishment and to make sure the punishments matches what society knows as 'uncruel', though in practice it doesn't work out as well as imagined.

I'm not sure if anyone has appealed mandatory minimums on the basis that they are cruel and unusual punishment: They probably have research to back up their claim. This is probably the true reason they aren't unconstitutional - because you have to appeal and sue (sometimes pretty far) to try to get those turned over. The other option is for the public to pressure legislature into changing the laws, and considering the current climate in Washington, I doubt that is going to happen soon enough.