Second, a smartphone knows much more than a PC did. There’s an old computer science saying that a computer should never ask you a question that it should be able to work out the answer to; a smartphone can work out much more. It can see who your friends are, where you spend your time, what photos you’ve taken, whether you’re walking or running and what your credit card is. The sensors, APIs and data that are available (with permission - mostly) to a service you want to use on a smartphone are vastly greater than for a website isolated within a web browser on a PC. Each of those sensors and APIs creates a new business, or many new businesses, that could not exist on a PC.
Benedict Evans has an interesting take on the growing divergence between the modern mobile landscape and the PC environment.
The quote above struck a chord with me as it's something I notice on a weekly basis when I sit down to record podcasts at my Mac. After working on the iPad and relying on the iPhone 6 Plus as a companion device, the amount of information and workflows that I can't have on OS X is striking. Beyond entire apps such as Health, Workflow, and Editorial or utilities like the Meet keyboard and Siri, the fact that a mobile OS does everything for me at this point makes the PC obsolete and a legacy model for what I need (with the exception of podcast recording over Skype, but I bet that will be solved on iOS eventually).