Yes, there is a trend of HTML and JavaScript being used to produce the kinds of smoothly animated active interfaces that were previously only possible with plugins — and this will continue much further should in-browser SVG, canvas and video catch on*.
This is definitely a Good Thing: open standards, direct browser support and authoring simply by updating text files is a huge win over closed plugins tied to specific development environments.
But I think you give jQuery too much credit on this issue. Certainly jQuery.Effects makes a selection of simple animations more accessible to a greater range of web authors, but that's only a small part of what jQuery is for, and a small part of the range of interactive effects possible. There are many other frameworks than jQuery, and many of the more impressive efforts are using their own code rather than any framework.
It's the increased JavaScript performance of modern browsers, coupled with some new features here and there, that makes “rich” UI possible without plugins. Frameworks merely make using some of those features easier.
(*: Which largely depends on whether Microsoft develop IE to catch up with them or whether they shun such improvements as a threat to their own technologies like Silverlight. Although there will always be a place for plugin-based rich apps, Silverlight is more vulnerable to native HTML apps because it doesn't have the widespread penetration Flash has worked up over the years.)