If Harry was the heir of Gryffindor, why would the sorting hat want to put him in Slytherin? No, He-who-must-not-be-named may be the heir of Slytherin, but Harry has to be more of a hero all can identify with. I would be suprised if the title of "Prince" has something to do with anything we've read in any of the books. Starting with OotP, these last books will pull out all stops. the start may've been slow, but its all out from here.