The absence of a widespread urge to subject Saddam Hussein to an international tribunal is of more interest here. No doubt political reasons were involved, but the inability of the "Hang the Kaiser" movement in 1918-19 to achieve its goal is instructive. The fact is that Saddam Hussein was often acting in his capacity as the sovereign authority of the Iraqi state. At the time of the exile of Napoleon to St Helena, similar questions were raised and answered, as this quote, drawn from Chapter Two here, illustrates.
In this letter the Lord Chancellor outlines the legal status of the imprisonment of Napoleon for the private information of the Prime Minister. He frankly admits that the imprisonment of Napoleon is not a legal matter. To the contrary, he saw it as an act which in terms of the "Law of Nations" would be "excessively difficult to justify", primarily a violation of French sovereignty, made necessary in order to secure the safety of the world.
However, had Saddam not been president of Iraq, (say he had been prime minister) it's quite possible we'd be facing a very different situation.