The big difference is that with a hard button you don't need to look at the remote once your finger is on it, so you can easily press it multiple times. This also applies to the 'soft' buttons on previous Harmony remotes, where the labels were soft but the buttons were hard.

With a touch-screen button, you must press in the right place each time - there's no tactile feedback to tell you where you are, so you have to continually look at the remote to avoid pressing the other touch-sensitive buttons or paging the screen. This is a major pain when you're scrolling through your favourite channels on Sky, for example.

So basically, touch-screen buttons are only good for single-press operations.