DRAM requires periodic refresh to retain values.
I would assume in low power envs unused DRAM would smartly be kept off (thus avoiding unnecessary currency drain).


But then again, I have no idea how DRAM in low power works so I am most likely wrong (even tho my thought sounds quite logical to me) .

EDIT: no mentioning of dropping currency drain from unused ram it seems.

http://en.wikipedia.org/wiki/Mobile_DDR