PyPI has the "full" "pyxb" bundle uploaded (this is good, as the default could well be the "full" package). However, trying to download from "PyPI" (via "easy_install") causes the "pyXB-wssplat-1.1.3.tar.gz" to be downloaded from "sourceforge". The reason is probably the "download url" specification in the metadata pointing to "sourceforge".
"easy_install" fails after the download, complaining that is does not find a "setup script" in the download.
For "PyPI" management, I recommend to split the various bundles
into separate packages with the core as a common dependency and
each "bundle" as a separate package (depending on other bundles or the core). This would make is easy to fetch the correct bundle via "PyPI".
A good PyPI/setuptools integration is especially helpful when "pyXB" is integrated into a larger context with tight "PyPI" integration. I, for example, use it together with Zope/Plone which uses "zc.buildout" to "describe" a configuration. "zc.buildout" makes it very easy to integrate packages with good "PyPI" integration; on the other hand, packages with deficiencies with respect to "PyPI" integration and "setuptools" support can cause quite some headaches.