Interesting article. One area of lighting that I think is largely overlooked is thinking about how the lighting informs us about the atmosphere. Every CG scene, including the quick demo scenes of cities and barns in that article, proceed under the assumption that the air is dry and perfectly clear. When was the last time you were in a city or on a farm and the air was crystal clean? The air is always filled with something: moisture, fog, pollution, etc. Air always creates diffusion and saturation on objects at varying levels depending on their distance into the background. Where this is most noticeable is when the artist leaves it up to the background image to impart that sense of atmosphere but then the black levels don't match between the foreground objects and the background image. Or if there are lights in the scene, those lights are crystal clear rather than having some sense of volume to them. Also, don't think you ONLY need to worry about background saturation in large outdoor scenes --- they are just as crucial to making a great still life as seen here . Look at the contact shadows on the objects in the background compared to those in the foreground. DOF will blur the background shadow more than lighten them so this is NOT just the effects of DOF.
Honestly, crystal clear renderings are a bit passé (IMHO) -- a hold over from the days when computer lighting could only do so much.
Dave
P.S. My own lighting exercise to really push my lighting skills - no GI or HDRI used...all done with manually placed lights (old school)