How do decide which flavor of Android to develop an app for?

My research shows that Android 2.2 & 2.3 have the loin share of the market. But when developing an app should I keep the API level of the app 2.1 or go with 2.2+?

What factors are usually taken into consideration?

I use 2.1 (API 7) as target, and 1.6 (API 4) as min version.

This covers most of the Android devices in use today.

If I need to use some (optional)functionality from 2.2 or 2.3 I use it with reflection.

Here is example:

    // try to override the transition animation
    if (VERSION.SDK_INT > android.os.Build.VERSION_CODES.DONUT) {
      try {
        Method method = getClass().getMethod("overridePendingTransition",
            new Class[]{int.class, int.class});
        method.invoke(this, 0, 0);
      } catch (Throwable e) {
        // can not override transition animation, so do nothing
      }
    }