what is the touch thinger on the back supposed to do?
That's known as the track pad. Believe you me, I didn't agree with it either.
They got two analog sticks, directional pad, 4 buttons, touch screen, L/R buttons, and a track pad! It's like Sony is trying to create the next BOP-IT! lmfao
The track pad is a very innovated and unique thing to have. Why a track pad would be more convenient would be because:
1. You never use those fingers in the back
2. More importantly, a track pad in the rear would prevent your hand covering the touch screen if it was used for gaming purposes. I mean the DS mainly relies on using a touch screen. However, half the time you need to use the touch screen, your hand and stylus just cover the screen.