As far as socks go, Reb Moshe says it is not necessary to cover anything below the knee. Therefore, he says socks are only a chumrah and can be made of anything, since they are not really necessary at all.
As far as women who wear above the knees or elbows, I am not condoning it, nor do my wife or daughters do it, but perhaps we can me melamed zchus.
The halacha is tefach b’isha erva. An exposed handbreadth (4 inches) of any part of the body that should be covered is considered ervah.
So if the entire area above the knee is shok, then one would not violate it until a tefach was exposed, meaning 3-4″ above the knee, and the same for the elbow. (Note this assumes the tefach is a measure of length, not area as in square tefachim, since then, even a centimeter above the knee may expose more than a square tefach all the way around.)
If this is true, then perhaps that is why many frum women with tichels let it uncover an inch or so above the forehead, since one does not violate until a tefach of hair shows.