Your assumption that grain is an undesireable "fault" of the filmstock" is incorrect. Its an accepted aesthetic trait. Its wrong to assume its undesirable--true, there may indeed be some filmmakers/DP's who would, given the choice, have preferred a clear HD-like image. But you can't just assume that every example is like this--most filmmakers and DP's not only like and want grain, but at the very least accept it as part of the aesthetic of making a motion picture. It should not be "corrected" for the simple reason that its not a "fault" to begin with, just like black and white photography.