Speaking in absolutes is a bit of a gamble. Bear spray has proven rather effective to stop unwanted bear approaches, regardless where it is used. Its rather like a pistol, some people want to carry a gun to feel safe, others carry bear spray to feel safe. For me, I try to hike with people who can't run quite as fast.
While I would agree that its not likely bear spray will be needed on the AT, saying it will never be needed leaves no room for the exceptions.