What ever happened to 'Knock-off Wheels'?

One feature that some cars, mostly sports cars, used to have was 'knock-off' wheels. These were wheels placed on a single hub and were held in place with a "wing" nut and could be removed with a blow by a hammer. These were used on race cars and production cars like the early (53-67) Corvettes. I heard at one point that there was a law enacted that prohibited new cars from being produced and sold in the US with the 'knock-off's, because the wheels might simply fall off from improper attachment? Is this true?