I think there's an "Android Audience". Regardless of device, they/I want portrait and landscape, android look 'n feel (Actionbar, etc), desktop widgets, background push, and so on. There are fairly easy ways to support some new and old APIs without resorting to lowest common denominator, such as checking the version before making the API call, and reflection. It is a continuing support and testing issue to support "This works on 4.0+ only" features.

The big problem with testing is interacting with OEM and 3rd party apps for your own core app functionality. Such as launching an external camera to take a picture: who knows what camera app the user has installed, and what it will return back to your app.