Drybrushing is used on the raised bits, but if you do the same technique to a flat area, you leave a thin coat of paint. It gives it that blurred or soft look that the gun you posted has, and allows you to mix the tones as you add more layers.
I use a big flat brush with soft bristles for drybrushing. There's no trick to drybrushing a flat part. You might want less paint of the brush than if you were doing corners, but you just keep brushing it until it starts picking up color.
gmoff - I got your PM. You don't have an email address listed on your profile, otherwise I would have emailed you the video.
Anyways, my video won't really help you achieve a look like that gun. As Aj pointed out, that gun is mostly drybrushed and my guns have a different style. I do briefly demonstrate how I use inks, so if you still want it I can email you.
The basic process for a gun like that, or at least how I would do it would be like this:
Drybrush colors from dark to light
Blending ink (so in this case a red ink was used to blend everything)
Ink for grime effect (something black, brown, chestnut, maybe more than one)
Drybrush edges with light color
That's more or less how I do any of my guns, I just do a textured stippling technique instead of drybrush the whole thing.