This movement seems to not only be pushing the evolution of ECMA script but also the tools around building these applications npm, node, grunt, bower.
From my experience though, his trend though did not start within the last 2 or even 3 years, but 8 years ago with the release of Sencha's ExtJS Version 2.0. ExtJS is a library/framework for building web applications, ExtJS has evolved quite a long way from version 2 to its current version 5 evolving into MVC framework and in its latest incarnation a MVVC framework. The end result for these client side frameworks are that you work with web services and data (JSON, XML).
Moving the front-end/middleware forward though can be risky, you cant just move all your backend/middleware code to the front-end, there are some security concerns that can play into this.
For example if you never thought to secure your web service because it was only accessible on a private network by your web stack well you don't want to put the security itself into the front-end as it easily discovered by view the source of your javascript files. This is were OAuth type authentication comes into place. An authentication request is made to the OAuth server and if successful the response contains a token that is used in your web service requests and valid for a given period of time.
But with any luck this migration to the front-end will continue evolving and reduce the layers needs for creating complex websites, services and or applications.
