Think about how Apps has been criticised over the past few years for the lack of innovation on the iPhone and iPad. Small changes and the perception that the devices should look radically different every time have led many to perceive that Apple has no idea or is resting on an idea that already works, but this is obviously not the case.
What exactly can the company, or Samsung and the rest, do with the phone form aside from small enhancements that will eventually be recognised as creating extremely reliable and quick devices that work.
And this is even more likely in a device the size of a watch. Apple could get to 200m water resistance, a shatterproof screen, G-Shock levels of toughness, 2 week battery life and ever more improved health tracking, but there will come a point when it truly does become minor changes the like we see of currently in the traditional watch world.
I do see the health side becoming incredibly accurate (invasive even?), but aside from that what else do you think the company can do to keep people upgrading a product that has historically never fitted the constantly changing world we live in today?