Yup. I have heard nothing from them, which makes me wonder whether it has something to do with how you are registering. This is pure speculation with nothing to back it up, mind you.
I registered using my usual Ubuntu web browser, Firefox. After hearing nothing I started to wonder whether I should have registered with the IOS device I wanted to Fruit Ninja for. I already have it for iPhone, but around the time the announcement was made I bought the new iPad, as well. I would like to have a version utilising its strengths, and that announcement looked like a cheap way to do it. People there checked where we came from based on browser info or some such and if it was not a device Fruit Ninja is available, or from the app itself, no go.
Other things that came to my mind: too many registrations for them to handle (backlog), expired registration time.
No big deal...I'll buy it some day - unless a universal update comes around before that.