No mistake. The letter in the package begins, "Even though you didn't fly with us enough to reach our published requirements, your frequent travel with us makes you one of our best customers, so we're pleased to extend your Platinum Elite status for another year."
I'm not going to argue. At that level, there are enough benefits to make keeping it worthwhile. It's especially easy to get used to getting upgraded to first class whenever I travel; I think I only flew three or so legs last year in coach on Northwest aircraft that had a first class section.
Maybe I'll fly enough this year to keep the status honestly; if not, I kinda doubt they'll do it again.