I think Roo got most of the answers.
But yes, the g-sensor (vertical accelerometer) is aligned with what? An aircraft structural datum, not necessarily fully related to the aircraft on-ground attitude.
The on-ground attitude of the aircraft is affected by the fuel load, pax and baggage load, landing gear shock damper pressures, and I'm probably forgetting some.
Too late at night here, and I'm too lazy to do all the calculations.
CJ