ICS and JB bring UI enhancements. More importantly, there are apps that only work on ICS and above and will never be backported, Which apps are important to users, depends on the user. For instance, Brighthouse and TWC have cable apps that only work on ICS and above. And as time goes by, you'll find more and more newer apps will require ICS and later, especially since ICS itself was released 16 months ago.
But you're right, you can still make phone calls and you can still use 2 year old apps. But if all you care about is using just a phone, you can get one without paying for a smartphone plan for a hell of a lot less money. And while it's unrealistic to have the latest greatest software at all times for the term of the contract, the device at least should not be obsolete before the ink dries on that contract. While the device still mostly works as it did when it was new, the actual resale value has plummeted since the ICS update cancellation announcement, so much so that a decent protective case costs more than what the device is currently worth.
So when it comes to why people make such a fuss about ICS, aside from the cancelled update, and aside from all the marketing hype that went into the device that got people to buy it in the first place, and aside from the fact that ICS and JB are that much better or they wouldn't be considered updates/upgrades, some people like to at least be a little current. After all, why go buy a new computer when people will give you an old one running windows 3.11 for free? Who knows, maybe you can find an old Univac somewhere. While we're at it, why use anything new at all when we can go back to wearing animal hides and banging rocks together to make tools.
I should tell you about the security vulnerabilities as well, but I'm not going to. Sometimes the lesson becomes more valuable when the person learns on their own, even if it's with some rogue dialer hooking you up with one of those $100/minute pay per call lines like back in the days of dialup.
