While Apple's two wearables platforms are inherently different from each other based on how they are designed for different sensory inputs, the two are in fact complementary to each other. The Apple Watch is designed to take advantage of the wrist's superior line of sight. This explains the device's rectangular display, designed to show as much text and other consumable information as quickly and efficiently as possible. Meanwhile, AirPods are designed to capitalize on the very powerful notification capabilities found with the human ear.
Items that are currently given to Apple Watch, such as tap notifications, may end up making much more sense for a device like AirPods, while Siri responses such as location or sports scores make sometimes make sense to be shown on an Apple Watch display instead of simply through voice in the ear. Apple's two wearables platform may end up working hand-in-hand, or maybe I should say wrist-in-ear, to provide a seamless user experience based on the most personal tech gadgets that Apple has ever sold.
AirPods will turn out to be one of the more strategically important hardware products Apple has released this decade. However, you would never know it judging from the way Apple unveiled the device last week. I suspect that was intentional.