With the release of the iPad mini, iOS developers wonder how it will work to develop for the new form factor. Even though the screen is smaller, Apple kept the same 4:3 aspect ratio. That is why iPad mini apps will simply be shrunk down versions of iPad apps. As the iPad mini uses the same resolution as the non-retina iPads, iOS will use 1x graphics.
Even though buttons will be smaller, if developers are already following Apple’s Human Interface Guidelines, that shouldn’t be a problem. The HIG recommends bigger buttons for the iPad than for the iPhone. Shrunk down buttons should approximately be the size of iPhone buttons.
Of course, if developers didn’t follow the guidelines in the first place, they will have some work to do to make their apps usable on an iPad mini. But there won’t be another category of apps in the App Store.