Topreads had originally launched in July 2012, and going on the coverage at the time it sounds like it was a fairly basic daily list of the most popular content. But with the relaunch TopReads is showing a better looking and more organized newspaper-style layout. We don't have any new details on how the top content is chosen, but the developers promise that they've "completely redesigned the experience and made the intelligence behind it even more compelling".
I'm never in short of new content to read, so I doubt that I'll ever use TopReads. But I'd also bet that I will be in the minority. The relaunched service is more intended to attract and keep the attention of current users of Zite, Flipboard, and other reading apps that offer an entertaining aggregated reading experience. Clearly Readability is hoping to get users of those apps to stay in the Readability app longer.