Current cellular mobile and wifi radio communications burn too much power for a battery small enough to fit inside a watch (unless you want to recharge it multiple times per day). So no completely independent watch-sized devices (useful ones) for this technology generation or likely the next few.
Plus, by being a generic iPhone companion, Apple would only have to build a single model instead of multiple radio versions like they have to do now for the iPhone.
had similar arrangements I believe. They could have sold so many more phone, if one could have just walked into an Apple shop to buy it unlocked. Customers are obviously willing to pay 500+ $ for a phone as we know now.