With dram, you have to refresh every cell within a periodic interval. Usually this is handled in hardware. It would be a crazy optimization if unused pages weren’t refreshed. There would have to be a decent amount of circuitry to decide that.

I can't imagine the iphone is entirely powering down memory. Otherwise just unallocating memory won't change the power consumption.

This is an argument for having less memory on a hardware level. But once the DRAM is there, it uses power, whether or not it stores useful data or useless data.

There's a reason why we say unused RAM is wasted RAM.

This is nonsense, at least on iOS. Apps get killed due to total system memory usage, not for power -- they only get suspended to save power.