In my most recent successful D&D game, pretty much none of the assumptions listed there really held true:
Correlon Larethian may have put out Gruumsh's eye, and you could probably have found a lot of people in the setting who would have told you that, but since no one there was able to communicate with gods or other planes in any way, it didn't really matter.
The Drow may have fought the other elves and been driven underground, but that also didn't really matter - since they arrived in the world, they lived underground, sure, in an impossibly huge cavern-country, but they were by all signs a regimented, militaristic army in heavy gearwork armor that lived underground because they liked it better there.
Acererak's Tomb of Horrors probably didn't exist. He may have built it, but chances are it was somewhere else beyond the scope of the setting.
Same with the Rod of Seven Parts - while it'd be funny and appropriate if a single piece turned up, there wouldn't actually be a way to quest for the Rod in the setting, so I rather assumed it wouldn't.
And this was a setting that actually had people from Greyhawk wandering around in it - so sure, a lot of the D&D tropes held true, but there were a heck of a lot that didn't, and that's not many changes compared to some of the more out-there homebrews I've seen running or played in.