Martijn
I think the reason you will see web apps being used is that people end up needing an always-online system that keeps check of feeds when their own machines are offline. When you have the server based system, it often makes sense to turn that into a web app.
Nkrs
That's understandable, though my take is that it is also convenient to use from a mobile phone if you set it up on your web host. I consume feeds on my computer, once or twice per day, so it makes sense to me to have it run and download stuff only when I am interested.