Well, to be exact, there still is an extra step between sketch and inked version - my original sketches usually aren't clean enough. Basically instead of inking the sketch over a light box I place a transparent matte film on it and do a quick trace with pencil, which I then scan and convert into ink. Using matte film results in a much smoother, cleaner line than you get with paper.

Sometimes I clean up the basic sketches with white-out and eraser to save that one step but that usually takes longer than just tracing the whole thing, and the result doesn't quite look like an actual inked lineart.