They are talking specifically, it seems, about RESTful and related API's, but self-documenting API's IMO should be present at other levels of an application too

They are talking specifically, it seems, about RESTful and related API's, but self-documenting API's IMO should be present at other levels of an application too. I would take it further and say that truly self-documenting API's should be discoverable by software as well as individuals. This is something we have worked on hard at LedgerSMB, doing so with stored procedures even (see http://ledgersmbdev.blogspot.com/2011/10/introduction-to-soda.html http://ledgersmbdev.blogspot.com/2011/10/introduction-to-sod... for more info). Anywhere there is a connection between software, this can be a good approach. Why limit it to the web?