Actually, Python isn't used for configuration at all, just for writing plugins. JSON is the configuration language. You can even change the menus in the app by editing the Main.sublime-menu.
The reason Python is used for the API is because the editor is cross-platform, and Python is the best choice for such a situation. If you want to run other scripts or programs, you can use the python subprocess module.
Yes, exactly, what are called plugins in Sublime Text jargon can only be written in Python. Thus for example, the illustrations of things you can do with the exciting plugin facility -- duplicating the selected text, or encoding the selected text with rot13 -- involve composing things in Python, of all things, else you are completely disabled.
The reason Python is used for the API is because the editor is cross-platform, and Python is the best choice for such a situation. If you want to run other scripts or programs, you can use the python subprocess module.
If there is something you are looking to tweak, http://sublimetext.info/docs/en/ has a lot of good info, and the forum (http://www.sublimetext.com/forum/) tends to be a pretty good place to ask questions.