It definitely is harder. I've done my shared of such web-application using GWT. This technique, known as the "single page application" is like writing a deskt

It definitely is harder. I've done my shared of such web-application using GWT. This technique, known as the "single page application" is like writing a desktop-app but with additional complexity such as maintaining a history on your own and deciding what "back" button action means depending on the context. The other additional complexity is the "offline" mode. Now suddenly you have sync issues. Pretty difficult even with frameworks.