They're only turning into operating systems because the operating system vendors, all of them, have gotten "deployment" completely and utterly wrong, and the web has got it halfway right. It's not that the web is massively good at deployment, it's just that everyone else is so bad at it that the web wins despite being worse as an app dev platform in almost every other aspect.
This is what the web does right that OS's get wrong: cross-platform development without any vendor lock-in (not even dev tools lock-in), no installation required before using an app, no permission grants required before using an app, implicitly up-to-date without restarting the app (every click has the potential to load an updated feature), highly granular downloading of features on-demand (downloading the behavior behind every click as you are working, which is crazy when you think about it), and secure and reliable distributed computing. The only thing it gets wrong is offline support (HTML5 appcache doesn't cut it).
So, right now as a developer you can build your apps on a platform that gets deployment right (the web), or one that gets app development right (native). Someone will build a technology that combines those benefits, and people will use that instead of HTML/CSS/JS to build applications. I'm looking forward to that.
This is what the web does right that OS's get wrong: cross-platform development without any vendor lock-in (not even dev tools lock-in), no installation required before using an app, no permission grants required before using an app, implicitly up-to-date without restarting the app (every click has the potential to load an updated feature), highly granular downloading of features on-demand (downloading the behavior behind every click as you are working, which is crazy when you think about it), and secure and reliable distributed computing. The only thing it gets wrong is offline support (HTML5 appcache doesn't cut it).
So, right now as a developer you can build your apps on a platform that gets deployment right (the web), or one that gets app development right (native). Someone will build a technology that combines those benefits, and people will use that instead of HTML/CSS/JS to build applications. I'm looking forward to that.