Hi Choco,
It's probably to save confusion.
You could imagine the complaint if someone bought it for slalom racing and then was disqualified.
I think they are smart calling it Ultrasonic to remove it from the racing line.
The sails have the same problems. Freeride racing in QLD (two years ago when I last looked) was limited to a 8.0m sail and I have an 8.2. I know there is no point as my next closest is 7.2.
All these restrictions. Like living in the Nanny state.........