Corvo is not an honourable man....and PROUD!
Although it may be because I myself have Mediterranean background, I think the vendetta preserves honour far better than the English duel. Why? Because a man who wrongs your family, and challenged to a duel only fails if he is beaten. See, within the system, you dying in the duel is still more honourable than vengeance/justice for your family, which I can disagree with. A man of honour does put his honour above all else, yes, but a man who allows himself to die before paying his enemy back, rightly so I might add, has lost his honour, because he leaves a family that depends on him to perish without him, solely to preserve his image.
And that's the point isn't it? Image and Honour are not so akin as the English "Gentlemen" say it is, though what else would you expect from Elitist aristocrats who considered themselves above everyone, not just commoners, but the Gentlemen of other cultures....seriously...