Greg, the Intermatic 7-day timer wall switches I normally installed used only AA battery power. I could power them up, read the display and program them as well as cycle them on or off in my hand without any electrical connection. They had a manual override and could be connected for either single-pole or 3-way switching by installing a jumper. They also came in both a 15A and 20A model.
I have also installed the Honeywell and other Intermatic ones that have to be connected to line voltage in order to power them up, so I guess it is a design choice, possibly to extend the two CR "coin" batteries life by using them only for memory backup.
