This question seems to be related to the fact that all hardware/electronics that are connected to some kind of programmable device can be discussed on SO as long as you discuss how do use it (writes a program that uses the electronics).
But not questions about how to create the electronics/hardware.
Another example that suffers from this is embedded stuff and microcontrollers,
here it would be really nice to discuss questions on both the hardware and the software since sometimes you should solve your problem in hardware and sometimes in software...
My point is that maybe hardware/electronics design could be accepted at SO,
or maybe Jeff could find it in his heart that hardware/electronics could need a own site.
Note: I know you can't have sites for all things in the world,
and also that electronics may not be the biggest field in the world.
But maybe it is big enough since I don't believe that I am the only programmer that enjoys electronics as a good hobby :)