My impression when the IBM PC came out, is that they intended to create an open system. They published the schematics. They encouraged anybody to create hardware and software. Their BIOS was copyrighted, but others came out with compatible BIOS's that were not owned by IBM, and that's what triggered the flood of clones. By the time that PC's reached the 386 level, IBM wasn't driving the bus any more.

The Apple II was an open system, but creating a compatible BIOS that wasn't a copy would have been impossible -- even for Apple, because of widespread software that made creative uses of the variables and entry points in the firmware. the Mac was intended to be a closed system.