I think you are kind of missing what is going on with a lot of html 5 development. There is actually little need to communicate with the server with a lot of web apps. Like illustrator, look at Aviary (I think they use flash right now) but the application is in the browser but all computation happens on the client, the only communication with the server would be to save the file. I see this being the same way with audio/video etc. There is the overhead and the performance issues, but not really a delay.