the difference to me starts in the meta-state and the rendering processes.
So the real benefit of a SPA would be distributed computing, if you can reduce the page loads from your server infrastructure and use CDNs you can actually reduce a lot of traffic and decentralize it.
if you're smart and use p2p you and don't want to keep exactly track or in control of the structure you can even make it offline available with a local storage + workers and so on.
So that's where it can shine .... if the state does not have to be maintained on the server or eventual consistency is enough or you want to distribute between clients.
So for example a landing page SPA is a really stupid thing to do or a anything where publicity is business value. Google and all the other search engines want an XML-Dialect (aka HTML) to parse so they can scale they don't want to waste their resources by rendering and loading and rendering and loading and again ....
So are SPA the future .... I tend to agree with mev-rael I've built dynamic pages with dom manipulations while IE6 Support was mandatory so it's old.
It's still then and now is an essential part of web applications so it's part of the future.
Just don't try to replace things that don't need to be dynamic .... that's just a shitload of work and you're probably just make things overly complex