Yes, please keep this in mind: you have a fraction of individuals of one posting board (we have over 1000 people registered, and certainly not even 10% have replied positively here) saying, "yes, we want it."
That does not a majority (or reflection of a majority), make. It only says that these individuals would buy such a book, not that making such a book would be profitable for WotC. And it has to be profitable. You can't keep a company going by producing books, investing time and energy into writing and development, that don't sell.
Besides, what is wrong with the big massive tome they have already released, almost immediately after 3E came out?
It's huge! And as for crunchy bits - they are in every basic game book that has come out since. Prestige classes galore each class book tailored to Greyhawk. A compilation would be nice, sure, but likely not forthcoming.
That said, do make sure to buy what Greyhawk material they *DO* produce, let them know what you like (and what you don't) and do your best to convert other D&D players into Greyhawk lovers. Bringing in new converts makes creating new material more palatable.
What I don't get is: what is the difference between the fat gazateer guide and the FRCS, besides the prestige classes (which are available in other sources)? Isn't the geographical, political and cultural stuff really what you are after anyways? What is it in the FRCS that is lacking in the Greyhawk book that is making you folks desire a new one so badly?