Well, Intel has x86 MeeGo, but not using it. So it is not only OS power savings involved, but CPU architecture itself. For instance ARM11 CPU core is less than 1mm^2@32nm. This helps Samsung to integrate everything in a single chip and stack RAM&NAND on top of it, enabling NAS functionality for a 2.5" HDD enclosure, where Atom is not a SoC and needs additional chips to operate as a computer system . Look at a cheap docking station from Seagate :
