Apple didn’t make an arbitrary decision to withhold Retina on the Mini to save money, upsell more buyers to the iPad 4, or “force” the first generation of iPad Mini owners to upgrade next year. They chose not to ship a Retina iPad Mini because it would be significantly worse than the previous iPads in very important factors.
The tradeoffs of an iPad mini Retina display
Marco makes astute observations about the often non-obvious tradeoffs in product design. There are always compromises. However, the new Nook HD has a high-resolution display and presumably has more than three hours of battery life.