Just a quick speculation on why I think the Apple Watch will succeed. I think it will succeed because it will make important information easier and more convenient to access, and buyers who get used to it won't want to go back to a less convenient way of doing things (i.e., accessing the same information through your smartphone). Speaking anecdotally, I never wanted to go back to MS-DOS and command lines after I discovered the convenience of Windows and a mouse. Similarly, I never wanted to go back to Windows and Internet Explorer after using a Mac and the Safari browser (and I used MS-DOS and Windows for 20 plus years before switching to a Mac).
People don't willingly return to less convenient ways of doing things. If I get used to having certain important information readily available on my wrist, then I'm not going to want to give it up -- I'm not going to return to something less convenient and more intrusive (pulling a smartphone out of my pocket).
The author owns stock shares of Apple.