My guess is that those servers, which can be powered down, are not offered as spot instances at all. A spot instance usually pays less than half the price of an

My guess is that those servers, which can be powered down, are not offered as spot instances at all. A spot instance usually pays less than half the price of an on-demand, for the same power consumption. Offering servers that can be shut down at half the price would cannibalize the main deals the provider offers, and thus make no sense.