Many people, at least on O'ahu, live in urban areas with serious "heat island" going on. In those locations, if your windows catch the prevailing winds, you don't need a/c, or perhaps only rarely. If there are buildings or terrain blocking the breeze, however, you'll be more comfortable if you have a/c, or if you make some lifestyle changes that make it less necessary.

That said, when I lived there, my bills never approached that figure, even with a/c.