The theory goes like this: by the time the Apple Watch launches next year (Huberty is guessing this will be in March), there will be about 315 million people around the world who own an iPhone 5 or newer. Of course, the iPhone 5 is the minimum hardware requirement for compatibility with the Apple Watch. Then, if we were to assume that just 10% of those users buy an Apple Watch, we're already over the high-end 30 million unit estimate.
The thing is that even assuming 10% of users buy an Apple Watch might be a conservative estimate, because the wearable market is growing faster than analysts had expected. Huberty says that the newest estimates are putting the wearable market at anywhere between 530 million and 1 billion units in 2020. And, 14% of iPhone users bought an iPad in the first year it came out.
It should be noted that the estimates for the Apple Watch sales from the supply chain have been guessing somewhere between 30 and 40 million units, which would be in the range and higher than even what Morgan Stanley is estimating. Obviously, the price point and ultimate list of features will likely play a big part in all of this; but, we might be looking at a bigger year for the Apple Watch than had been previously thought.