>Rendering templates on the server is not expensive at all, that is completely untrue.

Vaguest statement ever. It depends on the complexity of the template and the templating system, also then that file has to be served either directly or through a cache. complexity++ It is harder to scale a server-side presentation layer.

If you don't think that is the case please expand on your statement...

edit; please don't cite Twitter as a case, they are not the norm.