Yeah, you're probably right, Simon.
(Geez, won't anyone let this thread die already?)
It looks like I am definitely going to start running a game sometime in the near future. (Two players committed, another probable, and it shouldn't be hard to find a couple more, eh?) I think I'm going to put some introductory material for my homebrew world on the web and get some opinions from the potential players; if they don't bite, I'll go ahead and run in Greyhawk c. 576. Use the developed history up to c. 580 as background events and, presuming the game lasts that long, develop future history as I see fit.
It's definitely worth the time to develop a homebrew; the trouble is, that would be just me working on it. How can I compete? For example, if I run GH, I'm thinking of starting in Keoland. And lo and behold, at
The Kingom of Keoland, there's many megabytes of useful data on the history, politics, and geography of Keoland. That's just for one kingdom in an enormous continent! It would take me years of work to duplicate that level of detail for any kingdom in my homebrew world. OK, since some of the development of it started c. 1984, I've got a little head start.

But still, Greyhawk has been in development since c. 1972, and literally hundreds of people, many of whom are much smarter than I, have spent a lot of time working on it. It's real hard to pass up the opportunity to steal, er, I mean make use of that development time.
I expect to be using Greyhawk. Maybe I'll even break down and use the 10 or so years of history that I'm less than thrilled with, so as to take full advantage of
The Living Greyhawk Gazetteer. But somehow, I'm just not happy. (Sigh. Maybe I'm just a born whiner. But I am
not,
not, a troll. Now excuse me while I go back to my cave to regenerate.)