As far as I know there's no LEGAL requirement to use strobes (Some aircraft, the smaller private ones) aren't even fitted with them. As far as the South African CAAs pronouncement on this (I think it's in AIC 21.2?),strobes are to only be used when on a runway and/or in flight, except when in cloud by night where the flashing may affect the night vision of the crew.
Most airlines' SOPs state that strobes are to be used ANY time you are on a runway, whether you are crossing it,backtracking or taking off or landing, as well as whenever you are in flight.This significantly increases your visibility to other traffic. You are quite right, the recommendation did arise from the 737/Metroliner accident and it makes excellent sense.
Oddly enough, the only airline I've noticed that seems to switch strobes on only once cleared for takeoff is TK...which makes little sense if the primary anti-collision purpose of strobes is considered...