Was it the curvature of the coordinate system you were using during machine install, or was it the actual curvature of earth's surface that was important here?
If you assume the vertical axis and gravity are aligned, over the distances our machines moved the deviation between the two is enough to matter when setting up the machine alignment. The measurements would only match if you accounted for the curvature of the earth.
Gravity's vector is not the same as earth's surface-normal though - if you stand at the base of Mt. Everest then gravity is slightly angled compared to the curvature of the earth at that point.