Windows has "Compatibility Mode" to support these things. Additionally there are layers and layers of Windows API – an app built against Windows XP may still wo

Windows has "Compatibility Mode" to support these things. Additionally there are layers and layers of Windows API – an app built against Windows XP may still work but it's not using the same tech as one built for the current version of Windows. This is part of the reason that users always had to install different versions of .NET, or part of the reason why Windows is a huge OS (API surface area, disk usage) in a way that isn't suitable for mobile devices. Yes MS are better at backwards compatibility, but everything is a tradeoff and they receive plenty of criticism for the direction they take. Desktop computing has different constraints and is moving much more slowly than mobile computing, so it's more feasible to maintain that compatibility.