User blog comment:Zelron/Soul of the Dragon (Why the soul gotta be black?)/@comment-4057437-20121015220735/@comment-4057437-20121015232454

Remember the comment we made about the similarity between a Dead Thrall turning to ash and a Dragon burning up to just bones?

Mainly, though, it was research into the the true nature of Dragons.

All human/mer/khajiit/argonians have immortal souls, so Dragons aren't unique.