By text and location the sidebar does not apply specifically to this example.  It applies to the whole page, 'This page contains the API reference information.'

Documentation for argparse is indeed a problem - both because of its complexity and how it is used.  Many other reference modules focus on the classes and their methods.  This is organized about one class, the parser object, and a couple of its methods.  It's really more of an advanced user's tutorial, making most sense to users who already have use optparse and getopt.  For them that initial example is appropriate, selling them on the power of this parser.

For beginners I'd focus on the tutorial and its examples.  Example or not this reference section can be overwhelming to beginning Python users.