I'm guessing the "type effectiveness alteration" earlier is a typo, especially since it would be weird to change the type chart in the middle of a Generation. If such a thing were to occur, I would expect it whenever the next non-Generation 5 Pokemon games are released...
Also, I didn't know that the Pokemon guides had so many errors as the prior posts are indicating... XD (then again, I've only used a friend's Ruby/Sapphire Version guide years ago, and I only looked at part of it...) Reminds me of the mistakes present in the Golden Sun/Golden Sun: The Lost Age guide by Prima. XD
I mean, they have changed the type chart before, with the transition to GSC (Poison being nerfed and the addition to Steel and Dark). Maybe they thought that Ghost was too powerful or Bug was too weak? Though, this does make stuff like VoltTurn much more difficult to stop (Golurk being a Pokemon that can't resist the combo anymore).
Yeah; it's been bugging me for a long time that the Poison-type isn't super-effective against the Water type. XD I'm also bugged by the Steel type strangely not resisting Water-type moves (although the Steel type has enough resistances already, so making Water>Steel isn't really necessary IMO).