If you structure an app (with any library) not to leak references

But that's boilerplate.

  That's Backbone.Events, which is the core how models work with changes, and can be mixed in to any object.

But it's messy out of the box for other parts of your app without boilerplate. You need to structure your events somehow. It doesn't take much code and the libraries that I recommend are very small.

I don't think Backbone necessarily needs more features. It's great for certain sites that uses Backbone in limited ways. I'm talking about making an entire website end to end in Backbone, something that most of your examples do not try to do. But if you're making a whole app in backbone, not just a feature or a widget, something with many many routes and regions that swap nested views constantly, you'll need a bigger library.

So, backbone alone is fine for apps that's mostly traditional / server based, with some client side features. If the entire app is built in backbone then you'll want to build on top of it. There are many many frameworks popping up around Backbone and they should be supported by Backbone. Developers clearly need them or else there wouldn't be so many of them.