Where does the extra battery life come from? The CPU? Graphics? Better RAM? Better wifi/BT? Software improvements in the OS and apps to use power more efficiently? Lower power screen?

Battery life is affected by such a multitude of components that it's hard to extrapolate savings in one component to the battery life of the complete device.

The damn beast doesn't even heat up when yes > /dev/null

Yes, but that has nothing to do with the RAM. Processors take a significant chunk of the platform power while RAM in almost all cases does not anymore.