In the past decade, enterprise software development has gone through a major paradigm shift. This shift was the introduction of middleware, a.k.a application servers. The objective of the application server was to break the client-server model and move logic into a middle tier where the application logic could be cleanly broken down into discreet, testable layers implemented with object oriented languages. This push to application servers was driven both by the acceptance of object oriented programming and by vendors eager to make boat loads of money selling their middleware to businesses.
One of the side effects of the push to middleware was that databases no longer mattered. The goal of middleware was to abstract out the database. The thinking was that you designed a clean domain model at the middle tier, and various ORM technologies would map that to your database. Developers, in theory, no longer had to be experts in SQL, DDL, stored procedures and indexes. Application servers were going to save us from all this, turning databases into nothing more than data sources.
Another effect of application servers was the introduction of server controls, or widgets, used to help generate HTML views in the MVC pattern. Examples include tag libraries, JSF and JSTL. The application server would generate the entire view and return the complete HTML document to the browser to be rendered to the client. Applications servers were just reinforcing a similar layer of abstraction at the other end of the stack. Browsers were simply windows into the views being generated in the middle tier.
It is entirely possible that application servers go the way of the dodo, being supplanted by simpler tools which handle AJAX requests. Web servers will serve the basic content (html, js, css) to the browser, which will then make the AJAX requests to populate the model of the application.
Another possible side effect of the marginalization of application servers and middleware is that databases could start to matter again. I would expect that a smart database vendor will implement connectivity directly via JSON, in the same way they provide JDBC or ODBC connectivity today. The browser will send AJAX requests directly to the database server, which will return a JSON-encoded resultset. Expect to see standardization around what the database JSON request/result protocol looks like.