The iPad Mini is going to be an odd device. It is, after all, effectively a ‘concentration’ of an iPad 2. The fact that it has iPad 2 internals would suggest that the 2010/2011 generation devices (iPad 2, iPhone 4 and, based on internals, the iPad Mini) will probably be continued to get updated to the latest version of iOS up until iOS 9. I assume this is based on the fact that the iPhone 3GS was released with iOS 3 and but it still received the following three updates. Because the iPad Mini was released with an iOS version two versions newer it would suggest that the iPhone 4 or iPad 2 may receive as many as five version updates.
When the iPad Mini was announced a lot of people trashed Apple because they were effectively back tracking on what Steve Jobs had said about 7-inch tablets. A problem that Steve had cited was that developers would either develop scaled up phone apps or scaled down tablet apps and either way they would be hard to be use. Turns out he was wrong.
Apple’s Human Interface Guidelines for iOS are a collection of lots of long documents that basically just encourage developers to make beautiful, easy to use apps. There is one explicit requirement that apps should use touch targets at least 44 by 44 points. A point on a non-retina device is one pixel, on a retina device it is 2 pixels wide. This means that the actual size for touch targets on different Apple devices are the following:
Basically Apple has sized the iPad Mini at incredibly convenient size for developers because it means that touch targets on full size iPad apps on an iPad Mini will still be above (exactly) the minimum iPhone requirement. The major benefit for developers is that they don’t have to effectively scale up their touch targets so that they are big enough for the guidelines on the iPad Mini. In theory targets will remain their current size on the full size iPad too. An alternative way of looking at it is that there is no way that the iPad Mini could have been smaller without it breaking Apple’s own guidelines.
Given that the touch targets are phone size it also suggests that Apple reckons you’ll be using the iPad Mini in your hands more. It is reasonable to sit a full size iPad on a desk or your lap, but that probably won’t be happening with the iPad Mini because you don’t do that with your iPhone.