I was wondering what the difference is between ColdFusion's built-in AJAX functionality and using a JS framework like JQuery?

It seems that ColdFusion ships with tags that can do fancy Javascript layouts and controls e.g.`<cflayout>` and `<cfwindow>`. If it can already do this then why would one want to look at JQuery? 

I'm asking this question because I have been given the task of making an internal CRM application which should have a 'rich' UI. I started investigating JQuery and ExtJS which do the fancy client-side UI work. However I also noticed that CF has similar abilities. Because I am starting from ground zero I was wondering whether to spend (a lot of) time learning JQuery or ExtJS, or cut down on my development time and just use CF's built in AJAX tools.

With some good design skills, would it not be possible to create a 'rich' application with CF's built-in AJAX controls and some fancy CSS styles?

Any advice would be greatly appreciated.