Or is it a case of regulations not keeping up with ingrained industry practices, as suggested in some posts?
Operations over oil rigs under Category B envelope do not protect from engine failures during the takeoff and landing phase even if you operate outside of the H-V curve. This is because in all the RFMs, the H-V envelope has been determined for a complete different type of surface and there is no possibility to determine a H-V envelope on this type of surface.
The NPA has been issued only to try to fix an operational issue through a bureaucratic approach and the possible revision of the basic regulation, if any, will never add any safety to these kind of operations.