Did he really become that cynical over time?
Approximate text of the letter:
"I am unhappy that you gave the game the maximum rating. Especially since games that are better might come out!"
Response:
"The rating is given at the present time; it is possible that better games will come out later, which will also receive the highest rating."
I think it's unnecessary to say that this makes the ratings of previously reviewed games "irrelevant," because they were good "at that time," according to this logic.
And there are various letters where they explain "for what reason" so much magazine space was devoted to WoW.