I do know a couple of people with an amazing control of this type of airbrush because that's all they've ever used, but they're not the norm. A double-action airbrush is more commonly associated with illustration. It is this control that allows the smooth gradations evident in airbrush work. The modern airbrush has evolved to the point where you can paint to a hairline width if everything is set up correctly. Go to the Downloads page, too, for links to our Tutorials.
Progress is inevitable, and the computer is as useful and versatile a tool as any.
There are many practical reasons, too, for the switch to digital rendering. Today's art buyers are immersed in the digital age, and are accustomed to the nearly instantaneous creation of digital output. Many studios have brought operations in-house, and I suspect that new people are too often hired with computer knowledge a priority and artistic ability a bonus. After all, the best way to get new systems humming is to put a pair of hands on them that know the OS and software. It's left to the software to make those critical decisions.