I guess I'm not understanding your point here. I mean, using the latest accessories usually does require an up to date computer, whether it's a Mac or PC; same for OS X or Windows. As an example, Kaby Lake will only run Windows 10.
Well, I'm going in the opposite direction here. Sure, only the latest version of an operating system will support the most recently released hardware. However, I have an old 2007 Mac Mini that I'm still using daily as an HTPC. Apple dropped support for the 2007 Mini in OS X several releases ago; but Windows 10 should be able to run on it (or so I have read), as will most distributions of Linux (Fedora, Debian, Ubuntu, Arch, etc.).
What I'm saying is that older computing hardware is still quite able to perform a lot of standard tasks quite well (browsing the net, managing e-mail, performing tasks like word processing or managing spreadsheets or databases). And under Linux or Windows, these machines still do! Apple computers could as well, if Apple wanted to continue supporting them; but Apple's business model doesn't work that way...
Besides, accessories and OS's are usually matched to the machine hardware anyway; running old versions of any one of them can bog down a system.
Operating systems don't quite work that way. Properly managed, an operating system will generally work better over time as the authors of the code work to increase efficiency and improve performance of the underlying algorithms. The latest version of Linux should run
faster on a 10-year-old machine than Linux did ten years ago, because Linux has improved during that time.
Certainly, commercial operating systems do tend to grow bloated over time, as companies try to throw in "amazing new features!" to attract new users. But the fundamental elements of a well-designed OS tend to remain stable over long periods of time, and as such can continue to be used on older hardware. If, that is, the designer of the OS chooses to maintain such support...
Again, I would hold up Microsoft to compare: they have discontinued selling Windows 7, they are discontinuing support of Windows 7 on processors up to Skylake over the next year, and they will allow KabyLake to run only Windows 10.
Oh, sure! But, you don't have to have a Kaby Lake CPU to run Windows 10. As it turns out,
a PC with a Pentium D processor and 2GB of RAM will run Windows 10 just fine.
Anyway, the question here is not whether a particular company will support an OS forever, but rather how quickly a company will drop support for older hardware. (In my experience, for one reason or another most commercial software eventually dies, either due to lack of interest on the company's part, or due to the company itself shutting its doors. This is a major reason why open source OSs like Linux and BSD now command much of the PC market and practically all of the smartphone market, as they have a serious seniority advantage over all current commercial options...)