That's a good point. It is not necessary to webbify all Desktop applications. The application that i was referring to is a complex desktop GUI application and the End Users are happy with the application most of the time. Customer is not intending to migrate this app to Web anytime soon.
For scenarios, where the Customer wants the desktop app to be converted into a Web enabled app, the present crop of Web UI development tools (read Javascript based Rich internet application frameworks in the market) are not good enough and still not at 4GL level (i.e. more plumbing needed and Datawindow, PFC like features are missing) and would take a while, not sure how long. Appeon, however, excels in bringing PB's 4GL capabilities to the Web and that makes it cool. It also solves scalability issues inherent in a two tiered app by converting the solution into a n-tiered distributed web app, even though the same can be achieved using a n-tiered distributed PB app.
I agree that there are more options in the market today for Native desktop development including iOS, Android based app development tools apart from Windows. Also, there is a need for cross OS development. i.e. Windows apps running in Android and vice-versa. Clearly, Web (read HTML development) may not be the answer in these scenarios even though some of the folks seem to be promoting this. Applications hosted in Cloud may be the answer in such scenarios. i.e. you could run a Android app from a Windows based Cloud and vice-versa etc and the technology is fast maturing. For eg., RemoteApp from MS enable Windows apps to be run in Android etc.