different apps from these companies are further along in there utilization of a decoupled architecture than others but most all are working to this end, Many of Google's "applications" completely rely on this approach, I cannot comment on their mainstay (search). But most of Google app are assembled via the browser (Gmail, Docs, Maps, Wave) Its core to their strategy, hence entering into the browser market and the rapid push for HTML 5. As for Amazon most ancillary portions of their offerings use a decoupled strategy. The last understanding that I had, was they where waiting for a concrete SEO solution before moving their main asset .com over. These are large companies with legacy code base so it is natural that this architecture is emerging in their new product offering and acquired products first and is migrating it's way back into the legacy code base. In another post I provide referential links to the subject.