What all these frameworks are trying to achieve is standardisation of UI, so that people get a familiar set of controls across applications and platforms (and for developers too!). But we have so many standards now! (Queue relevant xkcd). I think this is where browser companies (Mozilla perhaps?) could be doing a lot more. Instead of adding endless new features to CSS and Javascript - which only give us more options…
The problem is that visual elements are related to fashion, and fashion gets stale with familiarity. So it won't stop changing.
Fashion is the biggest problem with usability -- the pendulum has begun to swing back a bit -- I hope it continues