Well you're comparing phones/appliances to computers, so yes.
Windows has for many years now used a multiple-tier support strategy (the Windows Lifecycle policy). Microsoft supports an OS for 10 years, and during that period if they issue a service pack then they support the previous sub-version of Windows for 2 years. Windows 8.1 Update is about 30% of a service pack; the update contains a number of feature enhancements and on a code level it becomes a "base" OS that all future updates are built against. So unlike a normal security update, you can't skip Windows 8.1 Update and still get other security updates. This in turn can be interpreted as a violation of the Lifecycle Policy, as it's functionally a service pack and therefore Microsoft should continue providing security updates for Windows 8.1 (sans Update) for 2 years.
iOS on the other hand offers no such policy. You are expected to use the most recent version of the OS and Apple has never said any differently, full stop.
Never mind the huge difference between an OS for a disposable device, and an OS for computers that is expected to last for a decade or more and is interfaced with massive amounts of custom hardware and software. Unsurprisingly, the type of device and the expected use case for it is a big factor in how long an OS is supported and how OS updates are handled.