Oh sure. Sorry, didn't mean to imply that it couldn't. But, that being said, if I wanted to do Epic Fantasy I wouldn't use Greyhawk. The sweeping scale of Epic Fantasy, cast of thousands, fate of the world, grand stories are better suited to FR. You expect FR characters to hob nob (after a few levels anyway) with the great and good of the setting. In Tyranny of Dragons, for example, the PC's are sitting at the table with the most powerful leaders in the Sword Coast.
This isn't what I would expect in a Greyhawk campaign. Number one, if you set a table for ten of the most influential leaders in GH, probably two or three of them wouldn't survive the meal.

Someone's getting stabbed, poisoned, or otherwise harmed. Trying to get them to work together would be a Herculean task and it's just not something I would expect to see in a GH campaign. That's why I see GH as a much more S&S setting. FR leaders work together because most of the faction leaders are good or at least leaning that way.
That's the difference. GH is a far darker setting where everyone is out for themselves. Virtually no one is actually "good". States are just as likely to venerate a demon lord as they are fight one.