[laurenbee]

This is not entirely passive (at least, in my experience) because in order to get people to continue to buy your books long after they are published, you need to continue publishing (unless you hit the kindle lottery and are wildly successful immediately).

[CraigJPerry]

As in publish new revisions?

[laurenbee]

No, entirely new books/stories. New books can get a nice bump in sales if they make it into the "New and Noteworthy" list or if Amazon mentions them in their "New books in [x category]" emails. Publishing a revision to an existing book does not change the publication date.