[dreamcompiler]

Relative rotary encoders are much cheaper than absolute rotary encoders, and I expect that's the problem here. If the encoders were absolute, one could make them work just like a potentiometer (because potentiometers are absolute). Relative encoders cannot remember where they were last set because they only sense dp/dt, rather than position itself. So it's up to the software to remember the last position, and everybody knows car companies won't pay software engineers tech company salaries, so by definition car companies get B-level and C-level programmers, and the driver gets weird misbehaving audio in the car.

[wolrah]

While you are correct, if the knob was only used for a single task, most car stereos I've used in the digital era give multiple roles to any knob(s) they may have. In the common configuration with one knob on each side the default modes are usually volume nearest the driver and either manual tuning or rotation between presets nearest the passenger, but if you go in to the menus one will usually scroll the menu while the other one changes settings. You don't want to have your volume or station change just because you needed to tweak a setting.