This isn't even particularly unusual. Most of Europe can't or won't extradite people when a death sentence is a possibility for basically the same reason, including to the US - the only way for the US to get an extradition is through a binding agreement that the person being extradited cannot be sentenced to death. Actually, the Canadian Supreme Court case which found this to be unconstitutional seems to have involved an extradition to the US from what I can tell...