It has nothing to do with the Read More Button or text on that button.
Those "Learn More" buttons you can see on that link I gave you is generated from some javascript or PHP file externally and place on the page with a different link to another page.
Try clicking on one of the "Learn More" buttons it actually takes you to another pages on the website, whereas the "Read More" buttons just allows you to view extra text etc as you mentioned that was truncated.
What I'm tyring to establish here is how this code created such a great linkable button with rollover states.
Came upon this looking for an answer to something else but the answer to the original poster's question is the RokCandy extension is what is used to create those stylized buttons.