Thanks, I had not seen that. It was only by chance I found out.
I do find this very shortsighted of Hilton though. There can be many reasons why you do not stay with them in a 12 month period. In my case it was simply that there was no Hilton at my various destinations, and when there was, one was full, the other was considerably more expensive (and no breakfast/wifi included) than a 5* Leading Hotel with both included.
I think a 24 month period would be more appropriate but hats off to those programs where the points never expire. In fact I shall make sure I use my points this year and then concentrate my loyalties on those other hotel programs instead!