Except, of course, for the rather inconvenient fact for your argument, Boudi, that Jewishness was and is traced through one's mother's lineage. In fact, it would also seem likely that Mary was of the line of David as well, so the status of Joseph actually becomes largely irrelevant.
Isn't it strange then that a whole 17 verses of this god-breathed text are devoted to something that's 'largely irrelevant'?