I always wondered how the death penalty passed this test and I guess this is how. You can certainly say it's cruel but obviously not unusual.

Well the other way it passes the test is that it certainly wasn't abolished by the Constitution when it was written, so why would it be abolished by the Constitution today? Only if it got particularly unusual, at which point the Eighth Amendment would kick in to protect against one rogue judge meting out a punishment that had been largely abandoned by society.

I think the definition of what is cruel and unusual changes. When the US Constitution was written people were still being hanged, drawn and quartered.