Apple very smartly used an exact multiple of four (i.e., each standard pixel equals two retina pixels on each axis) when it went from the standard display to the retina display between the iPad 2 and iPad 3. The result is that a developer need only build an app and enable retina for it to look great on both screens. This also means an app will work fine on the iPad mini with no modification, because the mini's resolution is equal to that of the iPad 2 (although somewhat sharper in practice because the pixels occupy a smaller space). In short, apps need not be made specifically for the mini to work beautifully on that device.