> Why wouldn't I just get these with the rest of the binary packages in my linux distribution?
Just speculating, but it's probably the same as with Firefox plugins. If somebody cares to package them, they get packaged. E.g. I never use any Firefox plugins that are not provided via apt-get.
I'm sure, it's only matter of short time, until somebody implements Python or other languages support for the GNOME shell. The idea, that people have to use the one scripting languages already failed with Guile.