I'm 50, and a cardiac patient.
The fall detection is one of several big motivators for buying this (ok, I wore my Series 0 to complete destruction a few weeks ago). Were my pacemaker or mechanical valve to catastrophically fail (unlikely but possible), I very well could go from feeling normal to unconscious in seconds - in a condition where minutes may matter, and a 911 smart-auto-dial could make the difference. Yeah, it might not work - but it might, and as the odds of the scenario increase, so will the quality of fall detection software.
The ECG may prove useful. Yes it's merely one channel - and that's way better than zero channels. I've had numerous moments of "something feels odd, would be nice to record ECG right now." Recording something on the fly can let me eyeball the graph, and email a "hey, look at this" to the cardiologist without having to schedule expensive visits resulting in "well, you look fine now." Would have been VERY helpful when atrial flutter kicked in (heart wanted to run 350 BPM, pacer slammed on the brakes at 150 for 12 hours before walking (!) into the ER saying "something's wrong"); a visual, seeing an atypical pattern, would have been far more persuasive than "dang, heart is running fast".
Yeah, I'm younger than those who normally would have an active interest in such features. With a large market, there's a non-trivial number of us.
Yeah, it's expensive. So is a nice analog watch. While many are pinching pennies, many have saved well and can afford a feature-full watch.
Nobody is "betting the farm" on this. That's a ridiculous strawman.
This is, however, a huge step into the future. Many of us will gladly pay a modest (!) price to move the state-of-the-art into new realms.
$530 for a base ECG-and-falls-and-cellphone capable model really isn't that much more than a nice watch + FitBit.