Part of the issue, a bit tangent to your point, is that when dealing with thick client software, once a version is released you can typically expect it to be in the field for quite some time. Many customers are upgrade-averse and simply won't upgrade a piece of software that is working suitably for them. Software developers have a bad habbit of fixing one bug and introducing another. With a web-based application you essentially control the release platform and can change things behind the scenes.