The Stack improvement is About concat method, now truly standard, accepting arguments that are not instance of Stack or Array.
var s = new Stack(1, 2, 3);
alert(s.concat([4, 5], 6)); // 1,2,3,4,5,6
Since this method uses defined slice one, there is no more reason to redefine concat method in inherited prototypes. That is why ArrayObject does not need anymore concat method, for a total of 4 fast redefined methods, plus inherited concat.
ArrayObject is now the fastest extended Array constructor that returns instances of the same constructor, ArrayObject.
ArrayObject is, at the same time, the base to create every other kind of cool library, using native Array methods power.