The help text is misleading; never pass the "foo=" part.
Somebody could teach bitcoin to accept either getreceivedbyaccount foo 10 or getreceivedbyaccount address=foo minconf=10
First option is better if you do not intend to use GNU options format '--xxx'. (And it is easier to implement on C.)
But for the convenience of future users make better use a GNU options. Then can be written a good autocomplete for shell.
... but maybe we should just change how the help text shows default arguments or improve the documentation.