Like it or not there are content-oriented (aka "pages") vs behavior-oriented (aka "applications") sites nowadays. That is not a "vague buzzword", that is reality. The web has evolved from a content publishing platform to also include application publishing, deal with it.
Of course its not a clear cut line and there are huge grey areas. But there are extremes of these that can be clearly labeled as one or the other.
A blog is not the same as an in-browser ide (e.g. cloud9).
These are drastically different use cases and requirements.
jQuery is awesome for content-oriented sites, as is progressive enhancement. I use both myself when appropriate.
jQuery has no structure for more complex business logic - where is the MVC or the PAC architecture? Awesome projects like Sammy.js and Backbone.js are making this situation a lot better - but are still not a full solution like Ext.js.
Frameworks like Dojo, Ext.js, qooxdoo etc are awesome for behavior-oriented applications aka "RIAs". Progressive enhancement doesn't make as much sense here because there is no where near as much textual/semantic content to "enhance" in the first place. Needlessly applying a concept based around publishing content when there is no significant content will cripple an applications usability.
It was not a lie that Ext.js, esp 4, is accessible and supports standards such as ARIA. Here is an example of an Ext.js treeview with ARIA support that is usable with a screen-reader: http://dev.sencha.com/deploy/dev/examples/tree/aria-tree.htm...
I do apologize for calling people "haters", questioning their experience and using the word "fool". Admittedly it does not help to have a useful conversation. Nevertheless I stand by my points and if the earlier FUD on Ext.js is to be taken seriously those commenters would provide some pragmatic and truthful points.