I think there's a change happening, some new cars can be started by button-press when the transponder (replacement for the key) is somewhere in the car (e.g. in

I think there's a change happening, some new cars can be started by button-press when the transponder (replacement for the key) is somewhere in the car (e.g. in your trousers' pocket). And then, of course there's the other aspect that in some cases you absolutely want to be able to cut power to your engine. Wasn't that exactly the case with Toyotas drive-by-wire throttles that apparently made people unable to stop their cars? Still: When you look at the electrical system for, e.g. a commercial airplane, you'll see a dozen different independent power-supply busses that can be fed from each other, different engines, or batteries. So that in case of power-loss in one or a few of them, not all safety critical systems black-out. I don't claim that such complexity is helpful or desirable in a car, but with the majority of drivers relying on computerized systems it probably makes sense to make power supplies more redundant. {probably that's already happening, and I'm just unaware of it?}