> Webapps can never be as powerful as a desktop application

You're confusing technology with user interface. The primary difference between web apps and desktop apps in the future will be the idioms they use in their user interfaces.

Offline storage and various other HTML 5 APIs mean that there will be nothing a web app can do that a desktop app can't. Web apps might never be as efficient as a desktop app -- compiled versus interpreted languages being what they are -- but efficiency is much less of a concern these days. Web apps are often quicker to write, update and iterate upon, so for any given new application, the web version may have a structural advantage over the desktop app.