I imagine that with the increase in RAM they may have also increased the space allocated for swapping*, given many apps will now be larger in memory. It wouldn't shock me if the swap space was 1gb or larger - certainly desktop OSX gobbles up large chunks of disk space for swap, whether it is actively using it or not. Could be that iOS is similar?
*for the non technical, 'swap' is space used for temporarily 'moving' running program's that are not currently on screen to disk, so freeing up actual memory for active programs.