, ZippyV wrote

If you can make HTML5 apps that run on iOS, Android and Windows then why would you want to use Windows-only API's and limit yourself to one platform?

Why does almost everybody use a Facebook app on their phone (regardless of OS) when the website is just as available? The answer is the same in both cases: the end user experience is much richer when you work with a native app than can ever be accomplished in a browser alone and a better experience draws more customers.