The basic idea is to do all computation on the server and treat the web-browser as a graphical dumb terminal. All javascript event handling code is moved to the server, without sacrificing usability.
What's the motivation for this? I'd say that the given addition example definitely sacrifices some usability because it takes so much longer to evaluate than if you had computed it in the browser. It also seems like this would make your web apps less scalable, since even the most trivial client-side scripts would consume server resources on a per-user basis. (And how would you do something like a JavaScript animation using this model?)
Sorry if this sounds hyper-criticial. I'm interested in better understanding what makes Pliant unique. (Much of your website reads like an advertisement though, which makes this difficult.)