Playtonic do not have to refund you. There is no law or requirement for them to do so.
You can try using the Backer messaging system on Kickstarter to discuss a refund. Playtonic, out of their own will, have chosen to refund backers that opted for the now discontinued Wii U version through this system. However, there is no guarantee that they will (and I don't think they should) refund you for this situation.
Hope that helps.
I am locking this thread.