The new nano features a larger display (2.2" and 240x376). This is the same width as the 4th Generation nano, but 56 pixels taller. On a pixel basis, that's 17.5% more screen real estate.
Apple keeps putting bigger screens in the same size devices. The footprint of the iPod nano has stayed the same over the last four years, but this display has four times the pixels of the original nano.