If you visited code.google.com, you might know that many of Google's services come with a web API. With these APIs, one could 'easily' develop a desktop application or a website based on Google's existing services. Thus, Google acts like a web service provider and developers make use of these powerful services.
The based-on web service programming model might replace OS oriented programming in the near future. The browsers may not replace all applications. However, operating system will become less and less important and services become independent of OSes.