I think it has something to do with the manufacturer not wanting to have the battery run down. Notice that the Jeep line used to have an under hood light on a mercury switch. Not any more. That light used to cause so many batteries to run down/warranty repairs/roadside assistance calls, that is was more cost effective to cut it out completely. Plus think how much they saved just on parts and installation labor alone.

However, the Jeep Grand Cherokee does have 2 plugs on the dashboard. One with a pic of a key, meaning that it was only on with the key and the other with a pic of the battery, meaning that it went directly to the battery.

I think that the X-fire needs an auxiliary plug on the passenger side of the console for cells and radar detectors. I have a splitter running all my toys. And as you said it would be nice to have my cell charge overnight.

This car needs a serious facelift, as far as the interior for ergonomics and user friendly features.