hpst Some of your questions answered:
Of course Dell doesn't make the panels. They do make the drivers (hardware "driver", not "device driver") and power supplies though, and between their hardware and software tend to be the most benign of screens.
Why is a Thinkpad X200 terrible for you? One reason might be PWM - the Thinkpad X series was intended to be ULTRA low power consumption so their PWM is astonishingly aggressive, irrespective of whether you use the CCFL model (X200) or the LED model (X220). PWM doesn't bug me so much, so the X220 is one of the best laptops I've ever used. HOWEVER, there was at least one iteration of the screen that made my eyes bleed.
As for dithering... the OS produces output, the panel recreates it. They talk to each other - the panel tells the OS what its capabilities are. The OS can choose to disregard that and send it something different than its capabilities. And the panel can in turn throw out that data and choose to display differently.
I could provide more detail if you need it.