That's my gut feeling on the matter too. I'd guess that the difference between scooting and straddling should help to separate out tricycle control from bicycle control. Furthermore, smalls don't seem to have too much trouble going between balance bike and pedalled tricycle.
That said, I've always thought those three-wheeled scooters looked a bit rubbish, further evidenced by their usual position of being slung over a buggy or dragged along by parents, rather than actually ridden. I've no idea what they're actually like to ride, thobut.