This article hints that the number of relief pilots isn't mandated. Wouldn't requiring more relief pilots for longer flights be safer and ethical? I personally prefer airlines that overwork their pilots less!
I'm asking more about North American and European airlines, not just Asia.
As part of the agreement ending the strike, CAL [China Airline] pilots promised not to strike for three and a half years and the airline increased the number of pilots rostered for long haul flights. CAL now rosters three pilots on flights over eight hours, up from two pilots previously, and four pilots on flights over 12 hours, up from three pilots previously.