There are of course lots and lots of JavaScript learning materials both in print and on the web. I assume that's what you mean by "framework agnostic". And of course the better you know JavaScript the better you'll be able to use jQuery, or any of the other frameworks.
That said, framework specific tutorials are likely to be far more useful to the casual or beginner developer. In the "real world", while you can do everything without a client-side framework, it's a lot of effort (and ultimately means you're creating a new framework.) All of the browser incompatibilities hidden away by frameworks like jQuery or Dojo would have to be re-invented.
You can write windows programs in assembler, but frankly why would you?
In that light tutorials based on specific frameworks, while appealing to fewer people, is ultimately more useful to the people who do work through it. jQuery (and DoJo et al) are popular precisely because it lets you build better, more reliable, and more cross-browser-compatible web sites.
Rebecca is obviously a talented developer, with a strong bent towards sharing what she has learnt so kudo's to her - may she do much more, regardless of the framework she's currently using.
After using Mootools for a while, I was once more comparing it to Jquery, and was pretty lost trying to find out how to do date parsing and number formatting with the latter.
A search returns loads of plugins with no documentation, you don't know which one satisfies your requirements and is mantained.
I don't think the core of jQuery is really intended to provide anything in this area at all. I think the usual approach would be to use whatever you'd be using without jQuery.
I don't have that much experience with CodeLesson, though, so it would probably be best to hear what others have taken away from using the service.