Note: This does not concern iOS 8+, as it finally supports real scroll events.
ScrollMagic works just as well on mobile devices.
One big drawback is that mobile devices dispatch the scroll event AFTER the scroll is complete and not DURING.
To get support for on-the-fly updates the easiest way is to wrap all your content into a big container with the size of the viewport and scroll within it instead (like shown in this example).
Unfortunately this also results in loosing the scroll momentum. To see how you can preserve it check "Mobile Support (advanced)".