Defog Incomplete teachset

[Former user]

The Defog tutor is unable to teach certain pokemon Defog that could learn it as a HM.

Proof: http://i57.tinypic.com/33nhnc5.png

To help as reference, these are the list of pokemon who are supposed to learn it: http://bulbapedia.bulbagarden.net/wiki/Defog_%28move%29