It fails for me on 3.4.0rc1 and 3.3.4:

PS D:\> $env:PYTHONPATH
D:\Python33_x64\Lib\site-packages\virtualenv_support\pip-1.5.2-py2.py3-none-any.whl

PS D:\> py32 -V
Python 3.2.3
PS D:\> py32 -c "import pip; print(pip.__file__)"
D:\Python33_x64\Lib\site-packages\virtualenv_support\pip-1.5.2-py2.py3-none-any.whl\pip\__init__.py

PS D:\> py33 -V
Python 3.3.4
PS D:\> py33 -c "import pip; print(pip.__file__)"
D:\Python33\lib\site-packages\pip\__init__.py
(site-packages pip is after the wheel in sys.path)

PS D:\> py34 -V
Python 3.4.0rc1
PS D:\> py34 -c "import pip; print(pip.__file__)"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ImportError: No module named 'pip'

Could it be because zipimporter is not a complete loader?

>>> import zipimport, importlib.abc
>>> issubclass(zipimport.zipimporter, importlib.abc.Loader)
False
>>> pprint(set(dir(importlib.abc.Loader)) - set(dir(zipimport.zipimporter)))
{'__abstractmethods__',
 '__dict__',
 '__module__',
 '__weakref__',
 '_abc_cache',
 '_abc_negative_cache',
 '_abc_negative_cache_version',
 '_abc_registry',
 'create_module',
 'module_repr'}