Ah I see. Magic is ubiquitous, existing everywhere. And certain races are more sensitive to it than others. Gods and daedra are far more sensitive to it than mortals, which partially explains all the powers they have. I wonder what created magic though. Anu & Padomay fought and created the et-Ada. But when was the Aetherius created and filled with bright magicka?
First, a definition of terms: Magic(k) is the act of using magicka to effect some change on your surroundings. Magicka isn't exactly creatia. Creatia and magicka are definitely linked together, but I wouldn't go so far as to say that they are the same. They both are Anu-aligned substances that leak from Aetherius, but Creatia is used to create and stabilize, whereas when magicka is used, it changes. Anu vs Padomay. By this model do we have the saturation of magicka in Oblivion while maintaining the void-like nature of the majority of Oblivion, as creatia is finite where magicka is infinite, so to speak. If you want, the best anologue for magicka and creatia is that creatia is matter while magicka is light. As was warned earlier, don't take that anologue everywhere, but the ES world does use it especially when it comes to Meridia and her relationship with Magnus.
Aedra and Daedra are definitively other beings. They don't exist in the same manner as mortals do and so it's hard to classify them in terms of mortals. While it is true that Aedra and Daedra have a much larger ability to manipulate magicka than mortals, it is more to do with their vastly superior ability to manipulate creatia (mortals can only manipulate creatia through the towers, and some of that is because of an Aedra facilitating it, but let's not get side-tracked here) and their ability to, forgive the wishy-washy language here, be more in touch with either Anu or Padomay that gives them their powers. Magic is simply a way to change something. A more efficient way to change something is to directly apply Change to that something. It then very easily bends to your will. Similarly, you use Anu/Stasis in order to preserve something from being changed, or to create something from nothing.
On creation of magicka: Anu and Padomay clashed and where they clashed, we call the Aurbis/Grey Maybe/All of Existence. Aetherius lies just on the side of Anu, where Oblivion lies just on the side of Padomay, mythically speaking. Magicka is a property of Aetherius. It was created when Aetherius was created, which came about more or less only because the two 'forces' clashed. At least, that's my understanding of it.
Please note, that a good deal of that is my own personal interpretation.