This is due to their use of EMACSLOADPATH; see
http://debbugs.gnu.org/cgi/bugreport.cgi?bug=6401#48
http://debbugs.gnu.org/cgi/bugreport.cgi?bug=10208#25
+++
** New command line option `--no-site-lisp' removes site-lisp directories
-from load-path. -Q now implies this.
+from load-path. -Q now implies this. This option does not affect the
+EMACSLOADPATH environment variable (and hence has no effect for
+Nextstep builds.)
\f
* Changes in Emacs 24.1