15 minutes is based on a 10 hour battery life (at 11 hours, it would be closer to 18 minutes), and I'm sorry, but I can't agree that 15-18 minutes is meaningless.
Standby current is not operating consumption, and I note from Micron's own data sheets that their read/write current is far higher than the Samsung, at 115mW.
You are using DPD figures--i.e. no data retention--the pinnacle of dishonesty. I'm seeing idle refresh consumption at 4mW to 70mW, very much in line with the Samsung data I have previously posted.
No one is arguing that point.
And I dispute strenuously your foreclosing of that notion. Engineering considerations clearly matter end-to-end here, and though supplier availability and production concerns also undoubtedly played a role, I can't seriously believe that Apple would have gone to the trouble to shave down the Cortex A8 while ignoring completely the impact of RAM selection (especially since saving just a hypothetical 10% on the A8 would amount to less than 30mW, something that clearly had value to Apple, and I doubt they had the resources or ability to make much deeper cuts than that).
Edit:
More dishonesty. NAND flash and RAM are not comparable--RAM is in constant use, but NAND is read and written only as needed and quite infrequently in the grand scheme of things. NAND is also non-volatile--it does not require active power like RAM to maintain its state. All iPads have two NAND chips, presumably with comparable read/write power requirements, and thus comparable operating power consumption. An iPad constantly seeking from NAND would and does have considerably shorter battery life, regardless of capacity. In fact, along with keeping the wireless active, the constant NAND access is a major reason why an iPad pushed to its limits only lasts about 6 hours.