Sleep tracking is not something that most people do in a manner such as step tracking. You can't get up and make yourself sleep more unlike step tracking or calorie counting where you can make an effort to get out after dinner to reach a goal.... YMMV.
Really?!!! I wonder why Apple put it in, or why it's available on virtually every smart or fitness watch, or why there are standalone devices that track your sleep. Hint: because many find it useful and important (and yes, I have had devices to track sleep, among other things, for a few years now and find it a very useful measurement....
The three day "arbitrary requirement" is simply a reflection on the fact that the new Samsung Gear 3 can last three days (oh, and the Frontier version includes LTE, too), while the Apple Watch 2 still can't make it through a 24 hour cycle.
Guess which one is more useful, and which one can actually track my sleep patterns? BTW, I remember people like you arguing how "nobody needs apps" when the first iPhone came out....