I think the problem has more to do with event bindings and how they cause references between objects in the JS runtime than it does with backbone. However we found that consistency and patterns were a simple enough solution for this problem. It just takes a bit of double checking is all when you are writing code. In comparison, I would say objective-c's retain/release patterns are a much more difficult to understand.
Since you usually only want the listeners attached when a view is actually part of the page's DOM, would it be possible to monitor the DOM for when the view is removed and do cleanup automatically based on a DOM event? (perhaps using the mutation DOM events http://en.wikipedia.org/wiki/DOM_Events)
Maybe, but that would mean you also have a reference from the dom element back to your JS object that was bound in the first place. I've been wrong plenty of times though, would be cool to see someone give it a try.
Extjs solves this by abstracting the dom. When you want to remove a component from its parent, you call the remove() method and it handles all the dom unbinding behind the scenes. You never interact with the dom api directly. Adding content is done by calling the add() method of the parent and passing it a child component instance. It also decouples rendering from component construction. You can have an entire component hierarchy with operational events and fully interactive from the code's perspective, that isn't rendered to the dom at all.
