The black actually is more readable. The problem is that the author over-compensated to make his point and selected a dark neutral (#5-6) instead of a neutral d

The black actually is more readable. The problem is that the author over-compensated to make his point and selected a dark neutral (#5-6) instead of a neutral dark (#3-4). The simple answer is #0 black doesn't anti-alias very well and distracts the reader. Almost anything #2 and darker will look the same (for text), especially on cheap PC monitors. #3 range works best for print-like black and #4 will hint of off-print black. #5 is the beginning of "over-designed" fuzziness.