That's exactly why they did this. They can lock out 3rd party vendors and also force you to buy new heads at an interval of their choosing all in the name of "ensuring quality".
It runs normally without a head attached, so they must not be doing this yet. The architecture authenticates the body to the brush, which is the reverse of what you would do to lock out brushes. (A third party brush can get the password from the body and say "yup, that's definitely the password" and then the body thinks it's genuine. Meanwhile, a third-party body could use genuine brushes because a brush can't mechanically make itself not work. So there just isn't any lock-in here.)
The main feature this seems to be used for is to put the body into "whitening" mode if you use a whitening brush.
Keurig did the same thing with their later models. The coffee I used (SF Bay pods) just shipped a widget that tricks the Keurig into accepting the pod. I drink cold brew now, but I wonder if that cat & mouse is still happening.
