We're currently seeing around one new iPhone and one new iPad coming out of Apple each year, though. Don't forget iPod Touch, by the way. Sometimes they come with new features not available to older devices. They get released with three different storage capacities, and only some of your users will have 3G/4G on their iPads. The point is that in a year or two this is going to be a worse situation even for iOS devices. It's reasonable to assume that Android fragmentation will also get worse.
Where does that leave us? Well, I think Android is taking an interesting approach. A couple of the things in the Android SDK that help deal with fragmentation: - Standard UI components (eg. Action Bar for actions/navigation, Fragments for generic slices of UI, Layouts for providing guidance on how Fragments are to be arranged on different devices and screen orientations) - They provide a support library that can be bundled with apps using features from newer OS versions so that the new features also work on devices running older versions.