Different rice varieties have very different cooking times, also ratio or rice to water also influences the time, so the machine can't just estimate based on weight.
Simple rice cookers have only a 100°C temperature sensor (or switch) that turns off the main element once the water is boiled.
My question is what sensor do they use to detect the difference?
I did some Googling but couldn't find any info.
That's enough to manage a temperature curve and predict the last 10~15min of cooking (mine shows a time only 15min before the end), and doesn't require much input from the user.