I think part of that is the abstraction layers.. The apple][ had a really long lifespan. The IIe had a production run of 11 years and was a slight evolution on a 7 year old design when it was released. During that time you were free to run nearly any apple][ application (excluding the IIgs ones) despite many of them being 10+ years old. Their functionality wasn't reduced and you didn't have to deal with an OS that changed under the applications and dropped support for them. People understood the target and the applications were tuned for it (similar to game consoles).

The advent of hard disks, and installable OS environments changed the model. Outside of zOS, and maybe IBMi, there simply aren't any OSs that actually have provided a fairly stable OS API over time. Even windows has decided they don't care about backwards compatibility despite the fact that for most purposes the core win32 API present in win2k provides basically everything needed to host the vast majority of modern applications. Games might be the exception but people forget the directX was an install-able component until MS decided to tie to to the OS with vista).