The iPhoneOS does capture onscroll events, except not the way you may expect.
One-finger panning doesn’t generate any events until the user stops panning—an
onscrollevent is generated when the page stops moving and redraws—as shown in Figure 6-1.
Similarly, scroll with 2 fingers fires onscroll only after you've stopped scrolling.
The usual way of installing the handler works e.g.
window.addEventListener('scroll', function() { alert("Scrolled"); });
// or
$(window).scroll(function() { alert("Scrolled"); });
// or
window.onscroll = function() { alert("Scrolled"); };
// etc