It sounds dramatic, and has cultural resonance - I would guess that is the reason why it's phrased in this way, to fit the narrative style of the author, and the world of the novel, as Eric S said. 'He was as black a pirate as any that ever raised a sail' conjures up images for anyone raised in an English speaking country and reading books like treasure island etc. For me it has the sound of a tale told by old sailors in a pub like that featured in treasure island, just saying ' he was really wicked' or something like that just doesn't have the same ring to it. In the phrase used, the author effectively conjures up the whole world of pirates, seafaring, the feel of the imaginary world he is creating and so on.