Well, do you really care if your web application or mobile application runs on an 80386? But, to get more practical: The wider your compatibility surface is, t

Well, do you really care if your web application or mobile application runs on an 80386? But, to get more practical: The wider your compatibility surface is, the harder and more time consuming your software is to write. I once worked on a C# desktop product in the early 2010s where we had a requirement to support Windows XP. This prevented us from using newer features in C#, like the task API, which added a lot of complexity to our UI code. (It's much easier to write UI code in C# when you can "await" in one line instead of dealing with callbacks.) Another drawback (of remaining compatible with Windows XP) was that we had to stick with an old version of .Net, which had bugs. Specifically, we were making a XAML UI, but XAML support in .Net for Windows XP was buggy. Furthermore, we had to test our product on Windows XP, in addition to both 32-bit and 64-bit versions of Vista, 7, and 8. Eventually product management realized that it cost more to support Windows XP than the additional sales it would make, so they dropped the requirement. So, yes, "Who cases if it doesn't run on XYZ." Supporting "everything" often has real consequences and real costs.