There are two frameworks that come close to this, both of them are rarely mentioned and I am not really sure why other than the fact that they aren't "sexy".

First is SmartClient:

http://www.smartclient.com/

SmartClient has the best databinding support I've seen in a JS lib. Binding is automatic between server and client, between controls, and validation code can be written once. It also has the richest UI control library I've seen, full of controls that actually work and aren't just a shiny layer over simple code.

Second up is OpenLaszlo:

http://www.openlaszlo.org/

OpenLaszlo provides a much more raw layer for creating UX on the web, similar to the OP's complaints about not having a UIKit like API. Additionally, it provides a declarative language for laying out controls, and also provides expression binding, so you can say "the width of this element is always 2x the height of this other one" and the binding and event handlers are created automatically. Its declarative language is XML, so there are some nice homiconic properties you get by making it possible to return XML from a web service to generate UI elements. As a bonus, it can generate Flash or DHTML.

Edit: Of course, both of these frameworks have their downsides. They're horribly ugly to look at (out of the box.) The declarative language for SmartClient is really ugly Javascript, and the language for Laszlo is really ugly XML.

However, they've solved the hard problems and left the "easy" ones. They're both open source. If someone were to come along and clean up some of the syntax and add some real polish to either of these, I think they'd really be remarkable technologies.