my D945GSEJT with extremely minimal equipment (1 stick of low voltage RAM, 1 fairly low power USB drive) idles at ~9W AC (and 11w with a mobile HDD, more ram, etc), I find it hard to believe that and SNB equipment (mobile or otherwise) idles this low.
my eeePC (N280/945GSE based) idles (with the screen off) at ~9W
The chipset which comes with these boards was outdated when it was released, never mind now. Intel picked it because they could make it cheap I guess. Its power consumption only looks good when compared to desktop parts (it's a mobile chipset with a mobile CPU).
There are (more expensive) mobile Atom boards which consume less than 5W at idle and less than 10W on load.
There are reportedly Macs which idle lower, stock. And they're not fitted with Atoms but with proper CPUs. That's because they use expensive mobile parts.
On a budget, I don't think you can break 13W or even 14W with conventional CPUs.
a lot of the reviews i have skimmed through have the amd a8 consuming less at idle.
I bet none of these reviews have tried to measure the CPU's power consumption. Modern CPUs do not consume a whole lot at idle.
You can make boards with AMD chipsets which consume little power at idle. I have such a board (custom HP board, available for over $400 as a spare part).
They're probably simply testing boards which are more efficient than the boards people typically use (or even more efficient than any board that's going to be available for retail purchasers). The same thing happened earlier this year with new AMD CPUs as I mentionned. How many times can you fool a lot of people?