I have to agree that it's very nice (especially for corporations, university, government, etc.) when tech companies have a clear statement about life / end-of-life operating system support like Microsoft and most major Linux distributions do.
I think the situation with Apple though is a bit atypical compared to those examples since they don't sell or distribute the operating system for general use but only as part of their own hardware so it's more about hardware support. Apple is also a bit atypical in that they make their hardware hugely forward-compatible with future OS updates for so many years to come. From an IT perspective to me it's almost ridiculous how far back of hardware you can use with the latest yearly macOS upgraded operating system release. So although you can't tell what Apple is going to do in terms of your hardware two versions (two years) down the road, you always know what they are doing a year down the road so at least with the next macOS 10.15 Catalina this fall you'll be fine.
Also, with their pattern of how they drop off support models typically a year at a time, the good money presumption is that even for macOS 10.16 in the year 2021 I would imagine you'd still be good most likely, but anything beyond that point would just be gravy.
So really it is comparing Apples (lol) to oranges. The only true direct comparison to anything else would be how Microsoft specifically handles its Surface tablet product line (since that's very comprable to how Apple does things making both the OS and the hardware).
