Akatosh didn't sacrifice himself to create Nirn as the other Aedra did though. The other Aedra were conned into doing so by the Daedroth Lorkhan. (I think Daedroth is correct, he's a Padomanic or some such, not of Anu like the Aedra. Daedroth were created from the blood of Padomay for those who don't know. Not 100% sure on the Aedra, they came from Anu somehow I think.)
Aedra and Daedra are for all intents and purposes identical,
except in how they align themselves. Aedra are Anu-aligned et'Ada who gave themselves partially or completely to create Mundus, while Daedra are Padomay-aligned et'Ada who were selfihs bastards.
The two borderline exceptions are Lorkhan and Akatosh. Lorkhan isn't exactly an Aedra or a Daedra so much as just a primal force for change. In a lot of ways, he's more like the direct manifestation of Padomay than anything else--he's not
aligned with Padomay so much as he figuratively
is Padomay. Akatosh, for his part, is definitely an Aedra, but he didn't quite share the "death" of the other Aedra during the creation of Mundus, given that he willingly flung his entire spirit into Mundus and infused the entirety of the physical plane with his essence. This explains why, despite being an Aedric spirit and therefore not able to regularly manifest in any direct sense like the Daedric Princes can, Akatosh is still much more powerful than the other Aedric spirits. He literally
is Mundus--he binds it together, stabilizes it, and as long as it exists, he exists. It's sort of like how various people in the Shivering Isles mention that "Sheogorath
is the Realm"...for his part, Akatosh
is Mundus, the embodiment of its structure, stability, and vital essence.
...Ye gods, this all sounds horribly dorky.