I think you're misunderstanding what a single page app is. If a single page app is degrading gracefully when Javascript is turned off then it is probably not a single page app.
Say / responds with the homepage as per usual and /feed responds with a different html start point, but the same application code.
Using this technique you could create a site that responds to multiple urls with html and at the same time creates a SPA experience using a single js application (say, with backbone for example).