Originally Posted by
Fyersing
As someone else has already posited, we can't accept the Cosmology Chart provided by Chronicle I as being indicative of anything, because Blizzard themselves has already said that the position of the relevant groups is entirely arbitrary. The only truth we can glean from the pages are going to be found within the text itself -- which, interestingly enough, specifically states that in the beginning there was Light... only Light.
The absence of Light, as it slowly moved across the astral universe, is what created the Void. This is important because it shows that something can be created without needing to share any qualities with the thing that created it.
An additional point of interest is that the Chronicle I tells us that Aman'thul, one of the first beings in the physical universe, "possessed a natural affinity for the latent magic in the universe". The word latent, at least according to the OED, meaning "(of a quality or state) existing but not yet developed or manifest; hidden or concealed". It could certainly be that all things arcane-based are ultimately a combination of Light/Void, but as Chronicle I implicitly explains that it's possible for one substance to create another, without it being necessary for the new substance to share compositional elements with the original substance, it must then also be possible that the "latent magic in the universe" refers to a third, compositionally unique substance.
As I said, certainly a possibility -- but as we already know/suspect that anything deemed to be "Nature", magically speaking, is some combination of Arcane and Light, it seems unlikely that this duality is the case.