Apple sold almost half a billion iPhones over that period so roughly 5% of the potential target audience has purchased the Watch. Not a bad start but still a (lucrative) niche product.
Agreed... the attach-rate for Apple Watches to iPhones isn't very high. But did anyone honestly expect it to be? Not many people buy $300 accessories for their smartphones.
Having said that... Apple has been able to move more units than any other smartwatch vendor.
I wonder what the attach-rate for Samsung watches is? Samsung smartwatches are obviously compatible with Samsung's own phones... and Samsung is, and has been, the #1 seller of smartphones for years. In other words... there are A LOT of Samsung phones out in the world.
Samsung smartwatches can be used with other brands of Android phone too. (and even with iPhones to some degree!!)
So Samsung's potential target audience absolutely dwarfs Apple's potential target audience.
And yet Samsung's smartwatch numbers are a fraction of Apple's smartwatch numbers.
I think that's the more interesting case-study.