the apple watch is just one killer app away from appearing on 75% of the wrists in america.
that's all it'll take. When phones got email and cameras, suddenly every middle schooler in USA needed one. This will be the same. Once the watch does something so badass, so hilarious, so self-reassuring... everyone will have one.
What will that be? That, my friends, is the billion dollar question. Maybe it'll take voice commands, or project a screen/keyboard, or be a TV, or just someone so cool and creative we will say "how did we ever live without that..." It'll be something. Maybe it films your whole day lol, and you can watch it at night. Maybe it remembers shit for you. I dunno. But you can bet, once the watch does something the phone cannot - and once everyone gets all hot and bothered for that killer app, they'll sell a billion of those watches in 2 years.