Paul Rand (who was perhaps the best graphic designer of the 20th Century) would disagree with that "tip"
But while rules are there to be broken, they are best broken when you are skilled enough to know when it works to do so.
Most people who will read that article are not going to be skilled enough at graphical design to be able to easily decide when breaking this "rule" is an improvement and when it makes things worse, and so will probably benefit from paying attention to it.
Those that do understand when breaking it is really an improvement should go ahead and do so when appropriate.
The problem of course is that far too many people think they're experts.
http://www.paul-rand.com/foundation/thoughts_black/#.UCLgysj...
he also calls the shadows on a tree trunk black, so it seems he is not really arguing in favor of #000 but in favor of the use of very dark monochromatic colors, including true black. Also ALL of his examples are completely black/white or grayscale images of PRINTED or PAINTED objects, which naturally all do not achieve #000.
His views are entirely personal, as are our own. Personally, I found the #000 in his Next Logo to be the worst aspect of the whole design, since its extreme contrast suggests a low-tech print process or an old EGA screen incapable of more nuance. This is an aspect of most of his logos that I have never really liked, the same extreme contrast and blockiness that makes his IBM logo look more like an old ASCII display in someone's garage than the representation of a bold and powerful company.