The LGG was the Greyhawk sourcebook of 3e. Hell, I still use it. Is a great book, albeit soft-cover and cheaply made B&W art due to WotC stinginess. But it's the same as any other sourcebook. You either sought it out or you didn't. Regardless, it wasn't needed in order to play a D&D 3e game. WotC didn't expect anyone to learn about it online any more than they expected people to learn about the Forgotten Realms sourcebook, or the sourcebooks for 1e and 2e before there even was an internet.