The hardware is much cheaper, but it is also way cheaper to engineer, and because a touchscreen is a very one-dimensional interface, many questions don't even need to be asked. There's no texture, shape or feedback in a touchscreen, for example.
BMW is a good example. They started putting in that horrendous double wide screen/touch screen removing all buttons (the radio 1-8 shortcuts), temperature, heated seats, fan speed etc onto the screen.
This of course has made their dash design a lot cheaper. The only things remaining are:
Volume (which can be pressed for on/off/play/pause), previous, next, park-anywhere-button, front and rear windshield defroster.
One thing that is amazing about BMW's volume control:
It clicks, but the clicks don't corelate directly with volume change. It depends on how fast you turn the knob. Turn it 5 positions slow = volume += 10. Turn it 5 positions fast = volume += 5. To prevent you from accidently turning it too fast and blowing up your eardrums.
BMW actually seems to be quite intentional with details like this. For those who appreciate thoughtful human-centered design, it quickly becomes clear that many of their choices reflect unusually meticulous work and attention to detail. But I wonder if this is shifting, as fewer people seem to understand the difference.
Are there physical controls that mount on a digitizer? E.g. instead of a rotary dial on a potentiometer, the bottom sits on a digitizer that can translate the "touch" event into circular motion. Same with buttons, like with a keyboard membrane, but capacitive. Wouldn't that be cheaper?
That’s not addressing the right issue. Encoders and switches are not the expensive parts. What’s expensive is designing the dashboard with precise holes, before you actually start the manufacturing process, lining up the component with the hole and cap, making sure they actually work etc. Compare that to a dashboard of the new Tesla robo taxi, which basically has a complexity of a TV mount.
But you don't need to line up the holes if you can just plonk the component down anywhere and then program the software with the locations of the components after the fact.
Ford does this on the MachE and I think the F150L. They have a rotary dial for volume control and that is just mounted directly to the touch screen and uses some sort of wipers to make contact for the control surface.
