How can I replace this light switch?
Basically the only "HOT" is the black coming into the box from the Main. The switch is an interrupt to the light, which uses the electricity. So the way they have it set up is the switch is just passing the Voltage through from black to black when on, and creating an "Open" when it is off. At which point the light (or a plug outlet) would be off; this is where the actual Black/White setup in your mind really matters.