The plugins does _not_ require the core component to run or compile. A remote sever using NRPE is also using the plugins but without needing the whole web frontend etc. Nagios plugins should not be soley dependent on any of Nagios-core, NRPE or NSCA. If it could be dependent on one of the three it would be nice, but actually not required as the plugins can be used to soo many things more then with Nagios.
fixed in nagios-plugins 1.3.0