> They certainly are making money if I come and eat ice cream knowing they have free WiFi that I can use, and leave (without buying ice cream) if the WiFi doesn't work for me.
The key thing is recognizing that the WiFi is closer to advertising rather than the product – the same situation might arise if they don't have enough chairs, the bathroom is out of order, etc. Just as you don't build out 2,000 seats just in case everyone wants to camp out, you don't want to invest more in the WiFi than the incremental percentage of sales lost.
If enough people care about the problem and don't buy ice cream as a result, they will likely change their policy.
I don't think this will ever happen, most will buy ice cream and just leave or sign in with their Facebook profile, which is a win-win for the ice cream shop.
Likely this will just cause enterprising people to look for holes in the registration process, like tunneling traffic over port 53 (old), or any number of other methods, especially when you are talking about a unified login system that forces you to do something with FB.