I view modem engineering and patents as directly-applicable to their core business (selling iPhones) than an accessories manufacturer. Every iPhone comes with a modem, but not a Beats headphone. 1 billion paid for an essential component vs 3 billion paid for an optional, extra component.
What's the ROI on Beats? Apple's recent financial statement does not list Beats, just a general "Wearables, Home and Accessories" line. Their 2018 10-K has a line for "Other Products" that includes "sales of AirPods, Apple TV, Apple Watch, Beats products, HomePod, iPod touch and other Apple-branded and third- party accessories." but nothing specifically for Beats. Anything I'm missing on their investor relations page?
You are forgetting Apple Music.