There is a world of differences to consider when designing for web or designing for desktop applications:

From fundamental interactions to keyboard driven navigational paradigms to accessibility issues to screen layout to basic behavior and reaction of buttons, links, etc…we have to consider that a product with a rich client and a web client are two completely separate applications striving to assist the user in meeting the same goals. Of course, it is a little more complicated than that but perhaps it get us going in the right direction.