I think within your post right here lies a lot of the problem. There needs to be a really compelling to write something as desktop software instead of as a web app, so most people don't even bother to learn how to write desktop software in the first place.
Absolutely, the paradigm of 'client-software' is becoming ambiguous for most of the web people. 'Porting' an existing web app to a 'client software' is a very trivial work, thanks to stuff like XULRunner.
