Do the refrigerators have a Sabbath mode as well? Wouldn't you want the light to stay off when you open the door, otherwise you'd be turning the light on and off (causing work for the invisible penguin who lives in the crisper drawer).
How do you know that the light doesn't stay on when you close the door of the fridge?
Actually, my grandfather used to unscrew the lightbulb in the refridgerator before the sabbath began, so that when he opened the door, it would not cause the light to come on.
It was considered OK for lights to be on timers, and for things like the refrigerator, AC, or heating to be controled by a thermostat. The difference is that you are taking no direct action to cause "work" to be done (having the heat or AC switch on, or having the oven or refridgerator kick on).
Mark