This is a, if you don't mind my saying, 'frame of mind' that I understand, but you have to think about web applications differently. You are thinking from the point of view of the webpage: let's call this
My way of thinking is, that each class, ie Log In, Menu et al would be layered around MVC, so an event grabbed from the registra would in fact only return the XML/HTML/whatever to the View at the end of the day.
This is a View-oriented thought :) It is based on the assumption that an event triggered by one of the blocks on a webpage always results in that same webpage but with parts of the blocks changed. This is an assumption that is easily debunked. When a login block is submitted, the web app might display a page in a totally different layout that simply says 'Thanks for logging in! We are now redirecting you'. So what is the point then of going through all blocks to examine if one of them has received a request?
Would then be just to go through each event in the registra, one by one, and dump the output to the View.