The killer cutoff is if it's possible to write server apps for the platform in question. For iOS you can while the app is in the foreground, for Android you can

The killer cutoff is if it's possible to write server apps for the platform in question. For iOS you can while the app is in the foreground, for Android you can all the time, for Firefox or Chrome OS . . . nope, they are explicitly designed to be clients to something else. That may seem ridiculous, but the hooks are not there in Web APIs to do peer to peer communication for example, let alone peer to peer based on discovery of nearby devices. Chrome OS even lacks zero conf network support. Aside from Mozilla (who seem overly attached to the support of carriers) the people pushing the advancement of the web platform have zero interest in altering this direction, and in fact would prefer we go further in it. I would be far keener on FF OS or Chrome OS if they supported sandboxed node.js on the clients, and worked on extending the API from node.js, not the web browser model.