Yes, I think you are right. There are a lot of desktops apps.
But even if they were not, right now, the PaaS options like AppEngine or the new AWS Elastic Beanstalk are too restrictive and not mature enough to become a serious alternative for enterprise apps.
No, but many systems will be that much more likely to be replaced by something that could possibly run in the cloud. It'll become something actually on the horizon in ten years, as opposed to something unreasonably far off.
Too much existing infrastructure. Too many systems that aren't web-UI apps with cloud backends.
Maybe in ten years, this will be more plausible.