I would use reddit as a counter example.
Sure some the new features could be built without an SPA, but it would be much harder to do so.
They have a full wysgi for theming built in, a real time chat app, a video sharing app, multiple messaging platforms, and methods of bundling multiple subreddits together.
They added all this really fast, due to the nature of the platform being an SPA.
I have the same issue at work. Any given feature in isolation could be done simply as a jQuery plugin, but together the only way to make it seamless is an SPA.