I think that only applies to their mobile devices. I have had Intel Macs that can't run the latest MacOS but can still Boot Camp into Windows 10. Of course, this is all moot in a post-Intel Apple world.
Also, Windows 10 in 2021 is far from being exactly like Windows 10 in 2015. There have been a lot of changes, Microsoft just doesn't increment the major number any more.
If you're saying that Windows 10 from 2021 is Windows 10 from 2015 with "minor updates", you haven't been paying attention to Windows updates :-)
Windows 10 updates are probably bigger than MacOS updates.
This is like saying Mac OS X is 10 year old software.
I agree with the latter, but tell that to their previous default of 4gb ram and 120gb ssd (for so long) and 16gb of storage on iPads.
Every single device ever made has to make tradeoffs. No device can be everything to everyone. Apple has (correctly) identified that RAM is really not the end-all-be-all that people obsessed with specs seem to think it is. If you spend more time working on other aspects of the device you can get away with less RAM and still have a device that people resell years later for good money.
Would you have bought a MacBook air or pro in 2017 with 4gb of non-replaceable ram for $1000? No, because it's obselete and you know that. What if they told you it was a great computer, and you didn't know anything about computers? Probably.
It's just about scale for the time being, probably.
The M1 chip is now in 5 different devices. That is 100% worth not fulfilling everyone's RAM needs for the fantastic economies of scale and engineering simplicity that brings. They'll come out with an M2 soon enough, which will undoubtedly have more RAM and they'll stick in the iMac Pro, Mac Pro, and MBP 16" (and possibly "backport" to other devices).
That being said I just "downgraded" from an Intel 16" MBP with 32GB RAM to an M1 13" with 16GB RAM and haven't noticed much of a difference, even though I was regularly getting to 80-90% RAM utilization on my 16".