I asked Paul Boddie, who maintains the Debian package. his reply:
In the Debian package, various things are "Recommends" not "Depends" due to
Python packaging policy:
The recommended packages are not actually needed to run shedskin on Python
programs and generate C++ code, but some of them are obviously needed if you
want to build that C++ code, and others will be brought in with the second
set so that you can run that code.
Originally, I had these extra things as dependencies and was told not to do
that, so I stopped doing that, of course. :-)
thanks for asking!