That appears to be the case:

"""
P:\Projects\OSS\Python\cpython\ $ chcp
Active code page: 437

P:\Projects\OSS\Python\cpython\ $ PCbuild\python_d.exe
Python 3.4.0a4+ (default:995173ed248a+, Nov  1 2013, 09:12:43) [MSC v.1600 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import os, sys
>>> rfd, wfd = os.pipe()
>>> r = os.fdopen(rfd, 'r')
>>> w = os.fdopen(wfd, 'w')
>>> sys.stdin.encoding, sys.stdout.encoding
('cp437', 'cp437')
>>> r.encoding, w.encoding
('cp1252', 'cp1252')
"""

The test passes as patched if I do 'chcp 1252' before running.  Is it reasonable to patch the test to expect the default stdout and stderr encoding to equal ``os.fdopen(os.pipe[1], 'w').encoding``?  Doing so passes on Windows, don't know about various Unixes.