Although originally intended for document publication rather than application development, due largely to the vast commercial potential of e-commerce, the Web has gradually evolved into a platform for application deployment. Almost every personal computer today, no matter which company manufactured it or which operating system it runs, is shipped with a web browser. This means content providers generally need not worry that users have the necessary software installed to run their application. To understand why we've gone back to a centralized model we need to look back at the advantages of that model and see how the Web leverages those advantages. Deploying a client-server application to many clients running different operating systems can be problematic.
Web browsers provide the most ubiquitous application deployment platform available.
Historically, client-server applications have been difficult to install and keep up to date. When a user loads a Web page, on the other hand, he or she is loading it from the content provider's server. If the content provider wishes to update the application they merely place an updated version of the pages on the Web server. The next time a user accesses the page they will get the latest version. This is much easier than trying to distribute disks or give complex instructions to a user on how to download the latest release of a piece of software.