Before long, a Watch can also be self-contained, technically, but remains limited by form-factor: tiny display. Unlike Glass, it must remain accessory... or so it seems.

But consider: the iPhone is primarily a consumption device. In many ways, it is predicated on many use-cases not requiring a full computer. Is it possible a Watch-size device will similarly turn out to cover many important uses? Obviously, you can use it as a phone. For music/video. To read txt messages/short emails. Casual games.

It's a real consumption device (unless Siri gets unrealistically good). Maybe many web-site functions (i.e. the actual use of the website, not actual current website) can be delivered via Watch: lookup opening hours; store locators; product list/price/specials. Perhaps Watch versions, as we now have Mobile versions - and of course, Watch App versions).

Rather than tethering the watch to your phone and having the watch just being treated as another phone peripheral, you could just as well do the opposite: have the phone tether to the watch to serve as e.g. a keyboard and secondary display.