Earlier, it was believed that the additional column of live tiles, as seen in leaked images of the Lumia 1520, would be exclusive to a new breed of Windows Phone powered Smartphones with 1080p (1920 x 1080) display panels. As it turns out, that rumor has been put to rest. Windows Phone Guru Joe Belfiore confirmed via his Twitter account that the third column of live tiles is available depending on the screen size. Therefore, the Lumia 1320 with a 720p (1280 x 720) display will end up with an additional column of live tiles while the Lumia 1020 with the same (or rather, slightly higher resolution) HD display will have the usual number of columns.
For those asking-- 3rd column in start (and all the other related UI changes throughout OS) are for LARGE SCREEN devices only (w 1080p).— joebelfiore (@joebelfiore) October 14, 2013