Consider an apple at the top of a tree that is pulled by earths gravity with a force 1 N. If the tree were twice as tall, would the force of gravity be 1/4 as strong?
No, because an apple at the top of the twice-as tall apple tree is not twice as far from earths center. The taller tree would need a height equal to the earths radius for the apple's weight at its top to reduce 1/4 N. Before its weight decreases by 1%, an apple or any object must be raised 32 km--nearly 4 times the height of Mt. Everest. So, as a practical matter we disregard the effects of everyday changes in elevation.