Application development today is pretty different than it was just a few years ago. Most web apps now make use of hosted third-party services for features like search, maps, video, or translation (e.g., AJAX APIs). These services mean developers don't have to invest in massive computing resources to build these features themselves, and can instead focus on what is exciting and new about their apps.
Building in dependencies to third-party services or moving to a new hosting infrastructure is not something developers take lightly. Now, Google has announced a System Status Dashboard for Google App Engine that provides some of the monitoring data, so you can make informed decisions about your hosting infrastructure.