When you select "On" the camera time moves ahead 1 hour; when you select "Off" it moves back one hour. My D3s, D700 and D800e all behave that way. Perhaps the explanations that you have read are unclear.
Since DST application is different in different regions of the world, not to mention within the US, this seems like a sensible approach.
Having to change it twice a year also give you a chance to reset you camera's time, since these things aren't 100% accurate. My D700, for instance, has gained about a minute vs my D3s and my cellphone.