I should point out that this is a diagram of a resistive touchscreen - AFAIK the nano uses the apple preferred capacitive multitouch version instead.http://static.howstuffworks.com/gif/iphone-11.gif
This means; the layers don't flex and there is no need for a spacer layer (the 'dots').
That's not to say the pattern couldn't be in the touch digitizer. I haven't seen it, so I don't know. Besides the touch layer, and the LCD itself; another possibility is the backlight layers (reflective and diffusing, could have a regular pattern, or some light interference phenomenon.)