yes but how else are power companies going to lower the expected power usage if people dont slowly start adopting a more concious mindset to save power? If over the year everyone managed to cut down their electricity by even something as small as 5% the companies providing the power would have seen that over the last year power consumption has dropped and that they can cut back themselves.
thats the whole idea, as mentioned at least 10 times in the thread, of earth hour. Awareness so people can take steps, not to make a huge dent in power usage, so no, its not void or crap.