That's close to what Mr. Rosa says, for the same reason he says that the material of the nut doesn't affect the sound on a pressed string. And my logic has nothing against that.
That's interesting and I can sort of figure out why it's so. A string is a straight line between the nut and saddle but when you press it there's an angle in both directions. If the neck is dead straight and the action is the same all along the fretboard, the spot where the angles are identical is at the 12th fret, right in the middle. The steeper the angle, the harder it is to press the string down. Thus we make the nut end much lower, trying to get the angles match as close to the first fret as possible for the lightest possible feel. And we don't have to worry about the angle at the bridge end since we don't play past the 24th fret and there the angles aren't much different to that on the 5th fret.