Well, in essence each buff and nerf affects the interconnected web of cards that is the metagame. I understand Boingo's point of view, especially considering that decks are tested on a "chance-of-facing" basis.
If one card is buffed, then inadvertently so are cards that hard-counter it, as more people will use the former. More people using the card that is buffed means that their hard-counter will have a greater value for the same cost, as it was not changed.