The power consumption difference between 1GB and 2GB is far from negligible, both in auto-refresh (active) and self-refresh (sleep) mode.
It's a significant fraction of total power draw when asleep. You also have to account for PMU efficiency being pretty low when running at low current, so minor changes are an even larger difference. There's plenty of publicly available figures you can find to research this - find the "IDD6" self-refresh current in an lpDDR datasheet. Scale to the size of DDR you want, compare with battery rating adjusted for voltage.
It's a significant fraction of total power draw when asleep.
So a device with 2GB should have a significantly smaller standby time than one with 1GB, right, given that, by your claims, it's a significant fraction. Only that isn't true at all, and straight comparisons between, for instance, the GS3 international (1GB) and the GS3 Snapdragon (2GB) shows absolutely no reduction in two-week+ standby time. Of course all else isn't the same (it never is), and there are other power profile changes between them, but it certainly isn't remotely significant of a power draw.
Because in the profile of a smartphone it is absolutely negligible. Your phone is always in radio contact with the cell tower, that absolutely dwarfing all other power consumers. When you turn it actively on, the screen and the CPU absolutely dominate power consumption. There is no case where memory on smartphones is remotely a significant power consumer.
The iPhone has 1GB because that maximizes Apple profits. Every justification are like the hilariously silly claims when the iPhone was 3.5" so many had to justify why 3.5" was the ultimate size and aspect ratio. And it'll immediately shift again once Apple adds 2GB and a 5" screen to the iPhone 6.
Of course Apple tries to maximize the profit. I fail to find any business that doesn't try to do the same. It's called for-profit after all.
The question is, why doesn't Apple try to earn even more money by keeping the same A6 processor as in iPhone 5? Why bother to upgrade to A7 at all? Also, including an extra GB of RAM would cost Apple much less than upgrading to a whole new processor, don't you think?
It's a significant fraction of total power draw when asleep. You also have to account for PMU efficiency being pretty low when running at low current, so minor changes are an even larger difference. There's plenty of publicly available figures you can find to research this - find the "IDD6" self-refresh current in an lpDDR datasheet. Scale to the size of DDR you want, compare with battery rating adjusted for voltage.