The GUI world is a mess
Web and desktop applications, though maddeningly similar, have certain key differences. First off, there are two fundamental types of web applications. The first and the majority, are traditional hyperlink-based applications. They provide access to remote content using the familiar "document browsing" web metaphor. The second and the new breed, are desktop-like applications that create and manipulate complex content. They use the familiar "stay in the same window" desktop metaphor. Hybrids of the two are possible.
Desktop-like web applications, especially AJAX ones, are difficult to build, debug and maintain. That's why there is such excitement over things like web spreadsheets and word processors that, while functional, are so basic they would be laughed off the desktop.
This concludes today's edition of: Stating the Obvious.