I feel the need to note that Apple’s attitude to compatibility was always more nuanced than Joel portrays it in this post: they did actually try to maintain compatibility in classic Mac OS. They weren’t quite as obsessive about it as Microsoft was, and would sometimes deliberately break with the past to improve maintainability of the OS, but it was not in their interest to break apps and they knew it. To this day, there are hacks even in modern macOS to support badly behaving apps.
Apple’s approach to back compatibility was always give a stopgap to bridge generations. The irony is they would undergo heroics to support that back compat across generations (Mac 68k emulator, Classic environment, Rosetta, Rosetta 2) only to unceremoniously dump that work as soon as they could.
Microsoft can be almost religious about back compat to where long standing bugs won’t get fixed lest they break something (or special compatibility shims have to be built in to maintain those bugs for certain apps). You can’t run any Mac OS software from the 1990s on a modern Mac without emulation, but you can still run plenty of Windows software from the same time period as-is on a modern PC.
Of course one can argue which approach makes the most sense and there’s certainly merits to both.
