you overlooked refresh time, which is around 7~8 ms. So, in order to keep the DRAM data alive, DRAM should consume a few tenths of Watt per Gigabyte per second, it is considerable amount of power.
-refreshing is way (way) cheaper than streaming data out since you refresh an entire word line, and you do not pay io cost, which is a significant fraction of the cost of accessing dram.
