It seems to me that the same argument could be made of any web application that uses DHTML that reacts to user input. So even graphical buttons that change state based on whether a user is hovering over it or clicking it is an event that causes a change NOT handled by the controller. Even something this trivial would break the MVC pattern.
So maybe the more important question is to what degree or in what fashion is it okay to break or modify the MVC pattern. From my point of view it makes sense for events that invoke ONLY view logic to be handled by the view. So to have sort of a "Smart View" instead of the traditional dumb document or form that is usually returned in an MVC web application. This allows for much more responsive views that will immediately respond to user input. This level of responsiveness is not generally possible in a web application where events are processed over http.
So where do you draw the line? A "Smart View" should only contain view logic. There are obvious security risks to allowing business logic to be handled in the view so obviously that road is closed. I'm curious if this has been a common theme to others implementing AJAX on their web apps.