It's possible to have the same features by using multiple chips, but the advantage here is two-fold: cost and time-to-market. Combining several components into one reduces cost and the complexity of the device. It also takes less time to design and troubleshoot a new gadget.
Update: A commenter pointed out that I neglected to mention that the Kobo Touch uses the 508 chip. Whoops. While I'm on the subject, Freescale also provided chips for the K3, Kobo Wifi, txtr Reader, Irex DR800 and many others. They've been in the ebook reader market for a long time.
In case you're interested, Charbax of Armdevices.net got an early look at the new prototype platform that Freescale showed off which they've designed specifically for ebook readers.