In the case you use two hands, one for pointing and one for clicking, or just one hand with the thumb doing the clinking and the index finger doing the pointing, the Apple trackpad is NOT experienced any different from a conventional trackpad, and thus not a SUI. Because the user’s actions simply mimic having a conventional trackpad with separate buttons.

However, with single-finger operation, the button-action and the pointing-action melt into one single action. In daily use, this makes the interaction far more natural. Whatever my finger happens to be hovering over, if I want to affect it, I just push. Just like in the real world.

It is hard to come up with a quick good analogy, but think of this example:

Say you want to slide a piece of paper across your desk. In real life you just press your finger down and slide it around. Simple and straight forward. This is the way the Apple trackpad is experienced in daily use.

However, if the real world worked like a classic trackpad with separate buttons, it would work like this: Although you would be able to slide your finger over the piece of paper, the only way you could make it move would be to push the handle on your desk drawer with your other hand.

The technological difference is small, but the difference in experience is very important in this case

Move right finger over icon, press down with right finger, move while keeping pressed down, release. Very simple!