Gaming is fun, and fun is for everyone
...and this is where we get into the Dragonborn and Tiefling issues. Or, as I have seen it here, the "Kill on Sight" vs. "You don't me what to do" debate, which is incredibly tiresome. As I have repeatedly said, I don't mind the inclusion of additional races into Greyhawk so long as they are done in a way that respects the ethos of the setting. Some should be pretty easy (Tieflings as fiends, related to the whole Iuz issue), some may require more work (Dragonborn), but none are necessarily forbidden. What would be terrible, in my opinion, is (for example) placing large, non-human kingdoms in Greyhawk as that would be antithetical to the nature of the setting- which is focused on humanity. The main demi-humans are rare in most places, the rare demi-humans should be very, very rare.
This is nonsense. There are already several non-human countries within Greyhawk, so although I agree there is no need to add more, you will only be playing a "humano-centric game" if you're playing in a human kingdom.
But what if I play in a game set in the Orcish Pomarj? Or in the mountain of a Fire Giant? Or the Drow Underdark? The game would not be humano-centric, it would be centered on the race of that region.
I'll add, that Gygax himself expanded the number of races allowed within his setting in later iterations, and allowed more gods to reflect these changes.
In the December 1984 (Dragon) issue, Gygax mentioned clerics of non-human races and indicated that the twenty four demihuman and humanoid deities that had been published in the February–June 1982 issues of Dragon were now permitted in Greyhawk; this increased the number of Greyhawk deities from fifty to seventy four.