I think that many legacy players would spend at least some time comparing the beta to the 1.x game at a feature level, while new players would not. When Yoshi announced the alpha, he used the words "our internal testing is complete."

If we file defects in the beta regarding an otherwise functional feature that works differently than in 1.x, we're highly likely to get a works as designed rejection. If SE accepted feature change requests, the beta would span a much longer time than if they do not.