You appear to be suggesting that a temperature sensor and a MacBook in Power Nap mode use similar amounts of power. That is not the case.
Even in the webcam case, powering the camera CCD would take significantly more power than is supplied by the data line. You can derive this for yourself without taking one apart by realizing that the power is supplied separately for a reason.
Further, it's not the case that this would work when the power is "physically shut off". If there's no power then there's no power.
Even in the webcam case, powering the camera CCD would take significantly more power than is supplied by the data line. You can derive this for yourself without taking one apart by realizing that the power is supplied separately for a reason.
Further, it's not the case that this would work when the power is "physically shut off". If there's no power then there's no power.