RE: Why don't all radios have this feature? Add on if you have one.
As far as the automatic shutoff feature it could be added quite simply to shutoff at a certain voltage if the sticks aren't moving. If the sticks are moving beep, if not shutoff. As far as cost most the new computer transmitters would just need to be programmed and have an output port free to turn off the mosfet chip.
Actual manufactures cost to implement certainly less than $5.00. Most computerised transmitters are sold on preceived value that has little to do with manufacturing cost. Look at the features available on the Polk to get an idea of what can be available for a low price point.
I like Giestwares ideas.
John