I would be floored if this wasn't on purpose just because they have the ability to cash in on DLC with track and character packs. You know you're buying it. There isn't any point in lying about it.
I really don't think this is the case.
No character outside of King Boo is a significant hold out as far as the typical Mario Kart Racer goes (and he does sit out of the handheld titles), if they were going to do this then it would make sense to hold out on Rosalina like they are doing with Mario Golf.
I mean the amount of assholes who are super salty over King Boo, and even more those of us who would buy him as DLC have to be very low.