There's three chunks of code: the HTTP layer, the HTML view core, and the model.
The model deals with view-independant wiki level things, primarily retrieving raw pages and templates. (To do this it calls on a storage pools managed by a storage layer; the storage layer handles much of the RCS magic.)
The DWiki HTML view core gets a request context and is responsible for returning a response, whether that be rendered page content, redirections, or (rendered) errors. Renderers and template expansion are part of the HTML view core.
The HTTP layer is responsible for generating the request context, sending the response (including conditional GETs and other fun), and giving the HTML view core ways of generating proper URLs for given wiki pages.
The split between HTML view core and HTTP layer exists because the HTML view core is agnostic about how it is connected to the web, while the HTTP layer is intimiately tied to CGI-BIN versus Python BaseHTTPServer versus etc. So the HTML view core has everything that is web server independant.
FIXME: investigate this Python SCGI thing I've heard bits about. Or is that WSGI? See http://www.python.org/peps/pep-0333.html and http://wiki.python.org/moin/WSGIImplementations. Unfortunately on a preliminary look it seems I might as well write to CGI-BIN to start with.
I think that this is almost but not quite Model-View-Controller, but then I don't understand how MVC works (especially on the web).
To look at:
This suggests I am almost MVC except that my Controller is smeared over View code and that I have split the View into two pieces: the HTTP layer and the HTML view core.