From what I know for the standard change of spark plugs to be changed or can last around 100k km, manufacturer set standard at this mileage when they test run on the spark plugs at certain or consistent engine temperature, certain humidity level of the weather condition, condition of the engine and driving consistently at certain maximum speed/RPM (for example, only running at maximum 90km/h or around 2000+ RPM and not more than that to reduce temperature and wear & tear on the spark plugs).
Only at these conditions above, the spark plugs can only last around 100k km. If you are driving in Singapore with higher humidity and higher speed/RPM, the optimum condition of the spark plugs may not last 100k km.
This is according to senior Denso spark plug sales engineer I spoke to recently.