Keep in mind that 1G = 1 gravity, which is what you (and the X5) experience sitting quietly at the table.
You are probably expecting 'acceleration', but really the sensor is showing you the forces in 3 directions, which will include normal gravity.
Think of it this way - imagine using your game controller where you tip it to the left to turn a car left, tip right to turn right. You don't want to have to keep shaking/snapping (accelerating) to the left to keep turning left. You want to 'tip' to the left and then the controller is now idle, no longer moving yet you want to know that it is tipped left. That's why you'll never see (0,0,0).