The new UX in techcrunch. The tiny 'X' with a completion dial. Reason?

Was just reading on techcrunch when it caught my eye. The tiny 'X' there shows the % of the article I've read. Also, after completion, it changes to a tick mark. When this does, the entire page has changes state. Clicking this takes you to the home page. Why exactly has this been done? Just trying to understand the reason behind that. Any thoughts?