Always has been, and it's universally ignored. And it will continue to be ignored until a penalty is attached.
After 100 years, maybe we should try something different. I will grant you that the dumbell who approaches at 100 mph and passes on the right before you have a chance to move over should be shot, beaten, hanged, drawn and quartered and fined.
It's funny, but I have noticed more people respecting left-lane passing rules in the past few years, at least in the New York metro area.