In your documentation you wrote that when using current_user_can(), "..you can check for a specific role by inputting the role name instead of the capability name. It works the same way."
The WordPress docs advises not pass a role name to current_user_can() as it is not guaranteed to work correctly. See Ticket #22624: http://core.trac.wordpress.org/ticket/22624.
Appthemes has created a good alternative function to use: http://docs.appthemes.com/tutorials/wordpress-check-user-role-function/