Just installed the new GP 4.3 on my phone. The release notes state that Android 4.4 (KitKat) is required for GP 4.3.
So, I think that explains why my tablet - which still runs Jellybean - does not see the update. And if any of you are like the 49% of people still running Jellybean or earlier (
as of June 1), I think that explains why you aren't seeing the update as well.
For me personally, I don't care all that much about the terrain features, but it will be a bummer if this is the end of the line for Jellybean devices (i.e. if we no longer get any further bug fixes or other enhancements.)