Because easy_install/setuptools is not up to date.
Furthermore, setuptools is a bad idea anyway.
Somehow it packages the .so to a zip file which it tries to unpack at runtime at the user directory who built python-sybase. In server install it is quite often another user running it, and will lack rights to do the unpacking.
see http://www.b-list.org/weblog/2008/dec/14/packaging/
for more reasons to run away from setuptools.
Python Sybase 0.38 is again good.