That will probably be true if you are using Office 2020.
Then it's actually because the software is unoptimized. Not because the hardware isn't capable.
And either way, Windows 8's performance improvements over Windows 7 are evident enough that I think there is room for Microsoft to keep optimizing its softwares.
If Office 2020 ends up needing more hardware, then it's more likely because it's actually doing something other than just letting you edit texts.
Because until the day comes where my computer does everything I want instantaneously, there is room for improvement. Why do people switch from mechanical HDD to SSD? Why go from 2GB of RAM to 4GB?
I think it's very bizarre that you don't see why "high end" is always a moving target, especially this being a tech enthusiast forum. This has always been the case in every industry.
There is a very large difference between "nice to have" and "necessary". It's "nice to have" SSD over HDD, and it's "nice to have" more RAM, but neither of those things are "necessary".
If they ever become "necessary", then something is fundamentally wrong. I don't "require" my clients to have SSD or 4GB of RAM in order to get the best out of my codes.
I was giving you an example to answer your line about "needing" an octo-core CPU in 2020. You won't need one to write a document, but you'll probably need one to run the modern OS of that time.
Unless the OS does something fundamentally different (run a resolution that's a lot higher, has a 3D UI, or cook your breakfast for you), I think it's unreasonable to expect more hardware just so the OS is functional (not even talking about having good performance).
And since we are talking about that, I think it's safe to say that it's more because the OS is unoptimized. Not because the hardware is incapable. Again, I'll cite Windows 8 performance improvement over Windows 7 here as an example.
And I'll even cite Apple's Mountain Lion vs Lion here as an example.
Let's redefine what we think of as "high end" here, because I'm thinking "performance of both hardware and software", while you seem to think that "high end" is merely "hardware performance".