I am aware of this, although you seem to have the wrong pages. It is on p 31 (in brief) and then on pp 90 to 92 (in full detail) that the list of gods is found. But the word Greyhawk is not found. Nor is it found on pp 159-60 of the DMG. Which is my point: Tthese 3E rulebooks and supplement are not sources of information about Greyhawk. They are derivative of the prior work that actually sets out the relevant information about GH and its gods - including Boccob, and Lendor, and others - from which one can infer that their power does not depend exclusively or even primarily on their numbers of worshippers.
(Perhaps you are citing the 3.5 PHB? I don't have a copy of that volume. But it was published after the 3E DDG - I believe in 2003.)