<input required> and <input aria-required="true"> should both provide "error bubble" when input is empty; currently only <input required> does so. For legacy reasons authors should use the aria-required="true" as it has better support in screen readers. Since HTML5's "required" == aria-required="true" in the Accessibility APIs it would be nice if the visual output was equal as well.
<rdar://problem/10492155>
I think this is invalid. ARIA markup does not change the rendering behavior of the mainstream user interface. It just allows an override for the API.