WSF is just one example of how to implement a site using the Alfresco WCM functionality - it's by no means the only way to implement such a site. With that in mind, WSF 1.x is basically a simple JSP based web application that uses a number of content types (XML schemas) for handling editorial content as well as the navigational hierarchy for the site. It also makes use of renditioning templates for some of these types, reducing the rendering load in the runtime environment.
WSF doesn't require or constrain the deployment and runtime architecture in any way (with the exception of requiring a servlet container in the runtime environment), so it's a good way to experiment with different deployment topologies etc.
What other architectural questions did you have?