Gravitational acceleration (g)

Well, the difference sholdn't be that big, indeed, but you should know that the Earth's mass and volume has changed over the ages. The Earth is losing gases to the extraterestrial space (H, He) with very little impact on its mass, but the Earth's mass is constantly increasing by quite significant quantities of space dust. Another problem that may have an influence on g should be the variation of Earth's rotation speed over the ages, that also seems to have changed (a different extent of the terrestrial day has been calculated from the coral growth rings from the past ages).

Can you elaborate more on the rotation speed variation theory? How would it affect g?

Because of the Earth's shape, the rotation speed of a point from the Equator is greater than that of a point of higher latitude. Because of this variation of this angular velocity, you will have a different centrifugal acceleration for a body, greater on the Equator and zero on the Poles (because they don't rotate around the Earth's axis). This centrifugal acceleration is oriented towards the center of the Earth, thus decreasing the value of the gravitational acceleration. It's not a direct effect on the value of g, but more of the value of the acceleration of a body because of the principle of superposition (g - c'fugal acc.). It was a reckless choice of words when I said that g itself is smaller because the efect of rotation.