The content can change easily, so can the look. As discussed previously, look and content are the respective provinces of designers and writers. Few designers, lots of writers. One design, with variables, lots of pages. Change the design and the look of all the pages changes.
Pages assemble dynamically.
The designer can change the template without coordinating with the writers. The look of a site can be transformed with a single upload. When I floated this idea I heard that people think this should be done at the server, but I disagree. Been there, done that. The problem is that such systems are easy to set up, but hard to maintain.