Yes I am aware and no it is not the only difference, but yes the main difference is the integration of the touch panel as you have outlined. However that same difference is what makes the display superior.

For example, the Super AMOLED Displays have only one touch sensitive layer as opposed to the several layers (with air in between) in the standard AMOLED displays.

This is a key difference, as it means Super AMOLED displays are much sharper than standard AMOLED displays and are also more brighter as well (up to 20% more), again these facts are verifiable.

That is the difference between AMOLED vs Super AMOLED, showing Super AMOLED with its one touch sensitive layer offers a better, brighter, sharper display than the standard AMOLED in the N9, so the one difference you have outlined actually makes the Super AMOLED a better display.

The SGS2 however has a Super AMOLED Plus Display. The Plus is the key point. This technology allows the Super AMOLED Plus Display to offer more sub pixels than the Super AMOLED displays, (around 50% more sub pixels). Which again directly improves the sharpness of the display itself.

The Super AMOLED Plus displays are also brighter, thinner and more power efficient (by around 18%) compared to Super AMOLED Displays.

So the N9, has the standard AMOLED Display, despite the Super AMOLED display already being introduced in the SGS1 (which is already a big enough improvement to be considered a better display).

After this, it was further improved and introduced as the Super AMOLED Plus display in the SGS2, which is an even bigger improvement than its predecessor in terms of sharpness, brightness and power efficiency.

Again proving the S2 has a better display.