What's even more important is that Jace the Mindsculptor became quite unreliable as a wincondition because the amount of burnspells rocketed with the appearence of Delver of Secrets. Besides, there's the Punishing Fire plan which is used by most of the Maverick decks these days and which basically invalids Planeswalker (or Jace at least) as a wincondition in general.