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.