The site module documentation also described the Windows behaviour incorrectly.

Doc/lib/libsite.tex

@@ -16,12 +16,13 @@ search path.
 It starts by constructing up to four directories from a head and a
 tail part.  For the head part, it uses \code{sys.prefix} and
 \code{sys.exec_prefix}; empty heads are skipped.  For
-the tail part, it uses the empty string (on Windows) or
-\file{lib/python\shortversion/site-packages} (on \UNIX{} and Macintosh)
-and then \file{lib/site-python}.  For each of the distinct
-head-tail combinations, it sees if it refers to an existing directory,
-and if so, adds it to \code{sys.path} and also inspects the newly added 
-path for configuration files.
+the tail part, it uses the empty string and then
+\file{lib/site-packages} (on Windows) or
+\file{lib/python\shortversion/site-packages} and then
+\file{lib/site-python} (on \UNIX{} and Macintosh).  For each of the
+distinct head-tail combinations, it sees if it refers to an existing
+directory, and if so, adds it to \code{sys.path} and also inspects
+the newly added path for configuration files.
 \indexii{site-python}{directory}
 \indexii{site-packages}{directory}