These are places which don't actually exist on earth but are based on an alternate reality. e.g. Rainbow Six Vegas would be 'real' whereas Metal Gear Solid 4 would be 'fake'. This would help to seperate this giant page so you could know when real world locations are being used and when fake ones are.

Even if they're not on "real" Earth, their timelines branched off from the real world at some point, and had their origins here on Earth.

I don't think there should be a fake earths page.
Essentially all Earths in any game should be considered fake because none are exactly the same as Earth, it's all about the perception of Earth through the game, and the main idea is that it is Earth.

Nah, not really necessary.