I'm not saying web applications are always better (of course they aren't), but they are better for when you either can't/don't want to install any application that gives access to everything on your computer. If a simple navigation to the URL can give you the same thing as installing a application (implicitly giving them access to all your files and more), wouldn't you normally prefer the first?
Again, web applications are not better for everything, but they are more safe for the average computer user, as they run in a restricted environment, compared to native applications.
Again, web applications are not better for everything, but they are more safe for the average computer user, as they run in a restricted environment, compared to native applications.