The curvature of the surface of the moon doesn't matter, but the fact that the rock is orbiting the center of the moon just like a satellite would is the insight that Newton needed a smack on the head to get :)
Would I be wrong if I said that the deviation between the parabola and the elliptical orbit trajectories is probably much smaller than the tidal effect of the earth and the sun, solar wind and other external forces on such short trajectories? And as such the elliptical model is "as wrong" as the parabolic one?
After all, a model is only as good as the precision of the results it produces...
It's not numerical approximations I'm worried about. It's the fact that if you don't understand what's going on underneath, you're not going to have good "intuition" when someone asks a question like: what happens when you don't ignore air resistance.
