While catching up on newsletters from CodeProject, I came upon an interesting article talking about the "why" of JavaScript UI's -- not the typical "how".
Why JavaScript is Eating HTML
In "Why JavaScript is Eating HTML", Mike Turley walks through the "classic" static HTML for structure + CSS for appearance + JavaScript for behavior example, and then examines how this application evolves as JavaScript begins to control the application more deeply by interacting directly with the DOM.
Reflecting on this article, we've done this sort of thing before. Going all the way back to CICS to run terminal applications on mainframes, we've separated UI structure from behavior. Microsoft Access had its forms, which propagated to Visual Basic, and eventually to .Net, WPF, XAML, and so on. Static is easy, and frankly, it works pretty well most of the time, but as UI behavioral needs become more sophisticated, these static structures are ill-equipped to handle those needs.
So, I'm skeptical these techniques are going to put HTML out of business anytime soon, but in a dynamic application, they make a boatload of sense.