Santiago,
JSF is simply a UI technology that you can choose to use or not. There is no mandate that you "must" use it.
Personally, I really like what JSF has to offer. I also like other Web technologies as well - such as the ones you mention. Its even possible to combine several Web technologies to certain degrees with JSF. For example DOJO can work very well with JSF.
What I recommend for people curious JSF, is to take it for a
test ride and see if it fits your requirements. If not, feel free not to use it. :-)
-Chris