I don't think the quotes I'm seeing above are really representative of people who "get it" in terms of the role technology can have in improving our health. Yes, it is not a magic bullet. Yes, people will have to put forth some kind of effort on their part. But every hurdle that can be cleared is one less for them to trip over as they travel that path.
I know about 4 people who started using myfitnesspal and fitness trackers once they got their first iphones. One has lost 30 lbs, my boss lost 60, another guy lost 120 and the last guy lost 150 pounds and counting. It's pretty amazing - it's pretty rare for someone who has spent a lifetime overweight or obese to suddenly change those patterns without something dramatic. And simply having a tool that suddenly allows them to easily set goals, track daily/weekly/monthly progress against those goals, and enables them to more easily connect their short term decisions to their long term outcomes has had a dramatic effect that you simply don't see every day.
Will the iWatch extend that benefit in any way? Make it more accessible? I don't know. Certainly the idea of something connected to your body at all times with various sensors has the potential of increasing how conscious we are of that body. But I'll wait and see the device when it comes I guess -- don't understand why that's not everyone's approach.