>> With iOS and Android, you can't even transfer apps between them. That's good for developers (sell apps more easily to more people) and users (move apps around).
> I don't even know: to laugh or to cry.
> 1. You can create iOS app and sell it to [potentially] 250 millions of users.
> 2. You can create Android app and sell it to [potentially] 150 millions of users.
> 3. Or you can create "standards-based app" and sell it to [may be] 20 millions of users on desktop, tablets and mobiles.
No, iOS and Android can both run web apps. The potential market for web apps is 250M iOS users + 150M Android users + 20M web-based OS users = 420M users (using your numbers). And that's ignoring the web on the desktop.
A web-based OS *does* help right here and right now. Web apps can reach most users, the web is the platform with the most reach of any platform. That's great for developers, who can sell to more users, and also great for users, who can use apps from the device of their choice.