Looking at http://bugs.python.org/setuptools/issue1 and reading the
source of Lib/platform.py, it appears to me that uname() returns
different strings identifying the amd64 architecture depending on what
operating system is running.  It would seem to me that it would be
better to report the same arch with the same string on all platforms.

Could someone with win64 report the output of:

python -c 'import platform;print platform.uname()[4]'

Here is a patch against trunk that just replaces any 'x86_64' with 'amd64':

HACK yukyuk:~/playground/python/trunk$ svn diff
Index: Lib/platform.py
===================================================================
--- Lib/platform.py     (revision 75443)
+++ Lib/platform.py     (working copy)
@@ -1225,6 +1225,9 @@
         system = 'Windows'
         release = 'Vista'

+    #  normalize 'amd64' arch
+    if machine == 'x86_64':
+        machine = 'amd64'
     _uname_cache = system,node,release,version,machine,processor
     return _uname_cache