Well, it was really important for Apple because the II had all the software, and what came with the III was junk. They did have an emulator but it didn't do 80

Well, it was really important for Apple because the II had all the software, and what came with the III was junk. They did have an emulator but it didn't do 80 column at first. The Atari 400/800, had a sort of compatible successor in the 1200XL which wasn't compatible enough so didn't sell well. Succeeded by the 600XL * 800XL that were actually compatible. Those were followed by the 65XE/130XE/XEGS. The ST was a parallel different line. The IBM PC jr was just IBM being idiots with their product differentiation. Notice, it didn't do well because it sucked at compatibility. Amiga was bought. Compatibility was actually important when it the predecessor system was popular. Some companies didn't do it well.