We have this thing called a "society" which is empowered to make rules collectively. One way it is empowered to make rules.is through "laws" and "regulations". Amazingly, these things can and do work, often much better than free market capitalism.
When you buy something, you own it. If nintendo doesn't want to pay for hosting anymore, the ethical thing would be to dump the server code and the levels so that players can host the servers themselves.
Given how nintendo, activision, and other publishers have been acting the past decade, I really think its time for a Right-to-play law.