Remeber that the USA was founded on the idea of religious freedom. It was not very long ago that the LDS religion (Latter Day Saints) was considered a cult.
Apparently all that you have to do to become an officially recognized religion in the USA is to register it and then have a small group live in community for twenty years. Not a very big hurdle.
As for the decision being overturned anytime soon: I doubt it. Again it was a unanimous decision by a very conservative court.