I absolutely love to swallow cum after being fucked. I also love anal, and in many instances, would love nothing more than to swallow a load of cum after being fucked in the ass. However, i don't because of hygiene reasons.

That being said, i think i understand why the author of the story considered it to be a sign of ultimate submission for her to clean him after being buried in her ass. Anal play in general is quite taboo, so for a sub to not only go with that but do something that is even beyond taboo is, in my opinion, the author's intent.