It's not pure nostalgia for pre "web 2.0". We're moving further away from the ideal of separating content and presentation. This whole story is a consequence of turning the web from documents to application delivery, except that the applications aren't quite as good as their desktop equivalents. That would be fine if the applications were truly cross platform, but you still encounter sites that don't work properly on all browsers. Pages that go "oh sorry some unrecoverable error occurred: Please reload".
You can develop some nifty things with AJAX, but all it boils down to is a cool hack, because the restrictions are largely artificial, incurred as a consequence of deciding on a web application. We/re slowly moving towards a stable platform by adding layers to hide the complexity and browser differences. But all we're really doing is plugging holes in a leaky abstraction.