Gestures?
But another advantage of knobs is the ability to turn them, quickly and yet accurately, with thumb and first finger. Some even have push-pull gear reduction, to go between fast and accurate.
So you'd think that a GUI knob would use some analogous two-finger twisting gesture. With thumb and first finger.
Skeuomorphism worshippers have a lot of nerve to complain about abstract GUI philosophies when their own cult hasn't eradicated these design atrocities. Gosh, it sure looks pretty though...
From my own experience, knobs are far superior to sliders in audio applications, as all the adjustments are typically guided by hearing, and sliders' values can jump if you click in a wrong place. This just disturbs the flow. Most of the work with audio software UI is fine tuning parameters, often by a few percent, so relativistic nature of click-drag is perfect for this. Sure, there're relativistic sliders, but they feel rather unintuitive.