Web development is popular because it represents the highest reach for the lowest cost. This low cost isn't just about development. It's also about the cost of discoverability. Making it easy for customers to discover your applications is expensive. The process of downloading and installing is barrier enough, let alone the barrier of having to discover the source of the application download in the first place. For years throwing up a web application and paying for AdWords represented the lowest amount of effort to getting discoverability, although not necessarily the most effective way.
Enter the concept of the "app store". This is now becoming a replacement for Google, Bing, and Yahoo for discovering applications. App store searches are WAY more effective than web searches.
And when Microsoft is releasing all these nice apps for iPhone/iPad and Android before they do so for Windows Phone, I sure as hell hope they're at least using this third-party development tool that I speak of.