I've had phones that had something go wrong and they denied the warranty because the little moisture detection sticker had changed colors, even though the problem had nothing to do with getting wet.
I've also had a few phones die after legitimately getting wet. One time I fell out of the boat while fishing, another time I was fixing a water leak and got too wet, another time my son's phone fell in the sink while he was washing dishes.
This was all over a 15 year period, so it's not like it happens all the time. But I'm also a lot more careful than I would be if it was waterproof. I don't use it in the rain, don't use it in the shower, don't use it at the pool, hot tub, boat, fishing, etc.
I know a lot of you guys don't care about the waterproofing or lack thereof, but you're only 1 unexpected rainstorm away from a dead phone. Odds say it probably won't happen, but why take the chance at all if a "lesser" phone (the S5) has the waterproofing feature?
I saw Samsung announced a Galaxy Tab active. So that means Samsung offers waterproof phones, Ave waterproof tablets, but for some reason the Note got skipped.
Next time you're on a bike ride and it unexpectedly starts raining, it would be helpful if the phone was waterproof.
(disclaimer, I know nothing is ever truly "waterproof" and I use the term loosely, I really mean water resistant, at the same level as the Galaxy S5)