That's what Depp is doing right? Captain Jack Sparrow? It's a Keith Richards impersonation, but although Richards gets a part in one of the later sequels partly off the back of that, I don't see a credit for it in the first movie.

This is just how culture works. The pollination shades over from straight plagiarism, through homage and satire, until it's just unconscious assumptions and then it slips out of view entirely and even the creator has no idea it was there. Long before you disappear into the unconscious you're into a space where what you thought you were saying isn't what your audience understood at all. There are Warhammer 40K fans who don't realise that the Ultramarines are a joke. Yes they're blue, why is everybody laughing?