instrument lights and overhead lights should not be on the same switch

On my 2011 SuperDuty and just about every other car the instrument lamp dimmer and overhead interior lights are on the same switch, why/ These should be seperate operations. I should be able to brighten my dash lamps all the way without turing on the overhead lamps. There should be a seperate switch for this or a switch to toggle a dimmer between the dash and overhead lamps.
Martin B 12/12/2012
This is a great idea as the dimmer switch in my new 2012 F250 doesn't work good anymore as you have to change the dimmed lights to turn on the cab lights.