> So… what is supposed to attract users and developers to this platform [web technologies]? What they are getting not achievable on iOS or Android? What's the point? Have I missed it somehow?
One point is that this would be the only mobile OS whose development platform uses standard-based APIs. An example benefit of that is that an "app" for a B2G phone is just a web page (maybe with an app manifest file on the side), so your "apps" can travel with you from mobile phone to mobile phone, and from phone to desktop. 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).
Yes, there are better (in various senses of the term) development platforms. But none of them are standards-based. By far the best option for a standards-based platform is the web, which is why B2G, WebOS, Tizen, etc. all pick it. Only if you have massive resources to create a new development platform, or already have such a platform, do you not use it (and that is the path Google, Apple and Microsoft have gone). Otherwise, the web is by far the best option.
The web isn't everything, and native platforms are important of course. But we do need to keep some choice open in the market, if the whole mobile market is native apps on iOS and Android, we are in a bad situation. A more open alternative platform like B2G and the web would be a good addition. WebOS would be nice too.