Doesn't need to be that dramatic. Our Jeep got stuck in the Utah desert, and our guide had to pull out his Garmin satellite gadget to send a text message/coordinates for a friend to come pull us out. Lucky he had that thing. Yeah we could have hiked 3 miles over rugged terrain to a highway, but by the time we got there it would have been dark and we would have been exhausted. So we made the call. It wasn't life-or-death but it sure was convenient, saved us a lot of time, and allowed us to be back on schedule the next day. Definitely worth the investment. I'll be getting this iPhone for sure.
Good point. I did watch the keynote. SOS and Find My coordinates are the only explicitly specified use cases. But it's a paid service with the first 2 years free. I made the assumption you should be able to send text messages, because asking people to pay for a service that only lets you communicate with emergency services and that's all seems like a much less compelling product which is a bit un-Apple like. But then again, they have done lousy products before so it's possible they went with the less-compelling option.
Per a video someone else posted it seems there's communication with (probably just) emergency services which (for some use cases) is probably more useful than just a personal locator beacon.