The components handle their own input and render themselves, while the library manages the request/response cycle. The suggested approach allows creating embeddable login forms, checkout wizards, tabbed notebooks, or image sliders without using a separate portal engine.
According to author, the major differentiator of JSP Controls Tag Library from similar projects is the dual-mode nature of the components:
If XMLHTTPRequest is supported by browser, the Ajax engine updates page fragments in place, without full page reload.The article shows that creating componentized event-driven applications with a sensible approach to AJAX is totally possible with standard JSP technology. The same codebase supports Ajax in-place update for modern user agents, as well as full page reload for older browsers like Netscape 4.
The fallback mechanism ensures graceful degradation without noticeable effect on user experience besides a longer page update due to reloading the full page.
The only concern is whether Mr. Jouravlev has reinvented JSF without some of the features. :)