Django apps are supposed to be re-usable, but in practice they are not really pluggable. To integrate a app in your project, you typically need to read the docs (or source), figure out the "plug points" like urls, settings, templates, views, templatetags etc.. and then edit your settings, say a prayer or two and hope that it works.
An pluggable app should be more than just a snippet. It should provide a self-contained feature set with hassle-free integration. It should contain all info required to integrate it in a machine readable way so that the process of integrating it can be automated. Some of this info can be auto-generated by parsing the source and saved to a easily readable file, the rest would need to be filled up by the app authors.