A replica of the Earth basically just means you don't need a map (assuming you've got a basic knowledge of the globe) and things are distributed in annoying ways that don't make for enjoyable gameplay compared to a generated map.
I would like to combine Minecraft with Mount & Blade, so we could all have our own nations and raise armies and have big huge battles, but we have to find/raise horses first and craft our own weapons and all the other Minecrafty things.