User blog comment:Jack Pistol/Immortal Dovahkiin?/@comment-2040576-20121002202215/@comment-1080767-20121004044138

I agree that it'd make sense that only dragons can fell dragons, as Zelron said (inclusive of mortal Dragonborn, of course). It would also seem that dragons have a capacity to absorb souls of other, lesser beings, but are suppressed in doing so by Alduin, for whom it is "a privilege he guards jealously [or something like that]." Perhaps that would explain why Alduin's soul was not absorbed by the Dragonborn: Alduin's soul was tainted with too many mortal, Nord souls consumed in Sovngarde and the Dragonborn doesn't accept human souls. If that isn't it, other possibilities are:

-Alduin is an aspect and/or reincarnation of Akatosh

-Dragons can only absorb souls of lesser beings, and Alduin is at an elevated position in the chain of being over the Dragonborn

-Sovngarde magic

-There will be a soul-inception DLC set in Aetherius to kill Alduin...

Another question, then: Alduin's body is not left in Sovngarde like how other dragons will remain where they die. Furthermore, Alduin's death affects Tamriel, signified by how other dragons could sense Alduin's demise. This is no natural occurrence: something knowingly transported Alduin's body from Sovngarde. Who?