Sorry for not justifying my vote yet, I've not had time yet... but here goes.
This is how I see it: Middle Earth was supposed to be a new mythology for England and (not meaning to sound pompous or high and mighty) therefore this world. Therefore, I think that as Eru created Middle Earth (and hence this world) that he is supposed to be Tolkien's showing of God in the creation.
Doubtless, I'm wrong.