Thanks everyone, I didn't know there was a mediawiki-api mailing list. I found my answer in its archives:
https://lists.wikimedia.org/mailman/htdig/mediawiki-api/2007-November/000213...
which indicates that the docs are incorrect (not updated yet).
DanB
-----Original Message-----
You can probably get better answer by posting to the mediawiki-api mailing list.