Asking for one for the entire web is not a good plan because it would exclude competition. That's where the flaw in the argument is.
And while it'd be nice if browser vendors could just go off and improve along (from a browser vendor's point of view), it absolutely sucks for every single developer and the users. Surely, you remember "this website runs only on...". This is exactly what you see in the apps market - applications only running on certain devices, locking in the users. Sure, for you as a developer it's convenient. For users, it's a bad idea.