Adafruit RGB LCD w/ Shield kit connection to arduino uno?
The idea of shields is that they (in theory) can be stackable.
(In practice they are usually not)
This means that technically you can do this:



That's why by design every shield connects to every Arduino pin but uses only some of them. That way shield is mechanically well attached to the Arduino, and can pass "unused" pins to the shield above it.

Your shield is designed to be always "on top" so I think it only connects to some pins just for mechanical support. Technically the LDC screen needs only 6 pins and 1 pin per button.

EDIT:
I read now that the shield you got uses only 2 pins and communicates using I2C bus (which is perfect) so I'm 100% sure that it's designed to be on top of the stack and work together with other shields and uses extra pins for mechanical support.