What if someone came up with a new technology product that was hailed as a breakthrough with the potential to rival the smartphone, but then didn’t make it available to 85 per cent of possible buyers?

That is what Apple is about to do with the launch of its Watch. It will start collecting orders online from Friday and release the device in nine countries in two weeks.

For something that carries with it the best hope yet for a new “wearables” computing platform, the Watch risks being hamstrung. Only a subset of Apple’s existing customers will end up owning one. That is because it is yoked to the iPhone (which is used by only one in six smartphone owners): Watch gets its connectivity from the iPhone, and the only apps that work on it are extensions of the ones that are carried by Apple’s App Store for use on its own mobile devices.