[michaelt]

  I can't imagine the utility of low-power processors that
  "aren't trying to be energy efficient per operation"

Consider the Amazon Dash Button.

10 seconds a week running a WiFi radio, TCP/IP, SSL and all that. 604,790 seconds a week waiting for a button to be pressed. Battery powered.

If you can monitor a button on 1 microamp, and run WiFi on 60 milliamps, 50% of your battery capacity will go on sleeping and 50% on waking.

And wake-state power consumption is dominated by the radio module, so the best way to cut down on wake state power consumption is to make the wake as short as possible.

[forthfifthsixth]

That's the other side of low power devices, and part of the the beauty of asynchronous logic, it does nothing better then anything else! Computers like the ga144 'sleep' mid instruction waiting for a pin (button) to change, consuming only gate leakage for as long as needed.