The document they offer as a comparison chart falsely compares their framework, uses twisted numbers and mainly totally misses the point by comparing two totally different products.
Here are just few examples of the false claims.
jQuery has no MVC architecture: in fact there are a few of them to choose. I myself wrote one.
jQuery has no layout manager: how about this out?
jQuery has no Templates: well jquery.tmpl is actually now officially developed by Microsoft and unlike the flexibility that Extjs you can actually create true MVC views.
In conclusion Extjs is a nice concise framework, but gives very little flexibility to a developer, or even UI engineer to create their own paradigm. In fact, the way it is polished and powerful, it takes most of the fun away out of programming. There are in facts thousands of jQuery plugins which the community produced which the few ext widgets can never match in numbers.