I'd agree with the graph you've drawn there. I'm a big fan of TurboGears.

The reason I chose it was because it sits in the middle. It does a lot of stuff for you... but you can get rid of most of it when you need to.

Looking at web.py I think you'll suffer from the poor docs and the code can get a little hairy.

As a simple web server you may want to check cherrypy (which under pins TurboGears). It's got a good reputation, good docs and can be deployed in a variety of ways behind apache (or many other web servers)