The article contains some good observations, but I'm struggling to understand this one:

"Some sites try to communicate with Google through comments in robots.txt"

In the examples given, none appear to be trying to "communicate with Google through comments" - how is including...

  # What's all this then? 
  #   \
  # 
  #    -----
  #   | . . |
  #    -----
  #  \--|-|--/
  #     | |
  #  |-------|

...a "mistake" to avoid? There's no harm in it at all.