That's incredibly arrogant, and more than a little naive. The problem is that you're only looking at the small part of the problem which you understand better than the average person. Think about it instead from the perspective of the ice cream shop owner: they're not making any money from your using the network.
You might look at the a Facebook captive portal and think it's a poor choice but your solution isn't optimized for the business needs: cheap, reliable, doesn't require much staff time to support or special skills.
This particular problem is really a tech industry market failure, as there's never been a serious attempt to build a federated authentication system because the general trend has been trying to force a closed system on the world with the goal of levying a tax later. The most successful attempt was OpenID which was fundamentally mis-designed – inexplicably using URLs instead of email addresses – and quickly derailed by the gratuitous complexity crowd. There's a chance we might see things change with Persona but … I'm going to go out on a limb and guess that this won't happen quickly and, even if it does, it's going to be hard to find many developers willing to turn down a Facebook-scale salary to work on a turn-key level captive portal system priced at what an ice-cream shop can afford to pay.
I do not believe that the ice cream shop owner is doing anything wrong - he's optimizing his business to be maximally cost-effective to him. My complaint is about the current "reality", the system overall. We keep focusing on the average user, or on the most common denominator, cutting corners and making everything as cheaply as possible. This is not wrong. I understand the reasons why things are like that, but it doesn't change the fact that it makes me sad.
When you look at movies (or video games), you don't see typos, or subpar, broken, dumb tech. Because the worlds are animated by designers, everything is perfect and beautiful. Real life is not made by graphic designers, but I still wish there was a little more beauty in it. A bit less typos, a bit more caring about quality, long-term consequences and general look&feel. They say that perfect is the enemy of good. We live in a world of good enough. I just wish, on an emotional level, things were a bit closer to the "perfect" side.
(disclaimer: I grew up on Star Trek: TNG and later)
(disclaimer2: this comment is written after a few beers, so please forgive the lousy style)
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.
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.
It depends on previous context. Myself and another career programmer couldn't figure out how to print a wikimedia image on my uncle's Surface RT. (We tried several different apps and looked for context menus in each one to provide a print option.) As far as we could tell, it couldn't be done without dropping to the desktop. My computer-illiterate uncle showed us that you can just pick print from the devices menu in the charms. (Apparently, the Charms is a hybrid system menu and app context menu.)
I didn't have any context for how Win8 works. He did. Then again, I don't know how long it took him to figure it out and whether we would have figured it out eventually.
Despite my bad experience, I'd rather see radical changes in UI instead of sticking with what "works". It only works because we're used to it. Win8 might not be a step in the right direction, but it's might lead to improvements.
"Make a completely foolproof product and only a fool will use it".
The whole point of a context-sensitive menu is that it changes depending on your context. I think they're usually for advanced users -- often the right click menu just duplicates commands from the global menu but it's a faster access method. The Win8 case requires it for all users.
Of course if the context is the same, then the menu should be the same. (Maybe that was your point?)