On the surface, it looks like some of the toys may be more reliable than others - they really need to have skillful designers and coders to be able to pick up particular keys of the piano (I assume they don't have much to work with apart from vibrations).
The second part is that they are just complicated to make and not as robust as dedicated toys. Piano, or the foot pedals are examples - how many days of use until they fall apart? Will Nintendo fight copycats who provide cheap replacements?
Even if they gett all of the above wrong, I will forgive them if there will be a way to adapt or design your own gizmos and make them work without being an approved developer - this really does look like a great way to learn hacking.