Maybe you left them lying around e.g. left one at a convenient spot and did a drop and teleport to get to it and picked neither up? I have been known to forget the stones on occasion <blush>.
They are not mandatory - in fact I find them a minor benefit compared to DD where they were more essential. A few act 3 spots require them to reach but only minor stuff there (one key in one location and a cave with mediocre loot in another).
