The description applies for the plain authentication method. There you have the following line
if (($limit > 0) && ($count >= $limit)) break;
which will limit the output when you ship the limit parameter with a value greater zero.
According to the commit message
(commit) the default limitation intends performance advantages. If you propose to select all table rows then just set the second parameter to a big number.
Back to topic: I would add some information that the results of the function may differ when using backends != plain.