Comment by sdwr

I'm no apple enthusiast, but digital knobs solve a real UI problem. They:

- display a value compactly

- show that the value is modifiable by the user

- allow changing the value to use more screen real-estate than the knob itself

An abstract slider that works like a knob is jumping a knights-move away in design space from a traditional control. The user has to understand 2 things about the widget:

1. It's user-modifiable

2. It's manipulated by clicking on the widget, then dragging away

A knob is only 1 step away from a traditional control. You get the "user-modifiable" knowledge for free, because everyone knows what a knob is already.