I always believed in the "hungry enough" theory as well................till I met our granddaughter.  At least she was the reverse of what you've mentioned here.  She was lucky enough to successfully breast feed from day one, but never, ever, ever took a bottle, no matter what type of nipple or how hungry she got.  Didn't matter that it was expressed breast milk, it wasn't Mom and she wanted no part of it.  It made for some long tough times when Mommy had to be gone for something.  She weaned at about 13 months to a straw-type sippy cup.