You are not taking into account, distributed development teams or completely outsourced development of certain portions of the overall solution In which you have no control over the skill level of the developers.

As well, I am not proposing anything any more non standard than say JSP or Struts and Tiles. Their are plenty of AJAX frameworks that provide all of the bolts to erect this style of system without building and in-house system. Further, JSP is only standard for web development it does not take into account the variety of UI possibilities and that is the point of the matter. The UI much like the database is only a portion of an overall system. Just as you would not write you data-storage in your logic tier you should not be coupling the UI tier to your business logic.

There are plenty of sites that use this development methodology. Pick almost any mature "Web 2.0" site and they will be somewhere along in this evolution. Google, Amazon, Yahoo et. al.

I apologize in advance for being vague, but I would prefer to not loose my anonymity on this site and referencing my work would do so.