True. And my point was that IBM needed their (IBM) PCs to talk to their (IBM) mainframes - it was all in the family. Apple makes their hardware talk to Apple hardware. 3rd party vendors stepped in to make different maker's products talk across networks. It was necessary for IBM to make IBM components talk to IBM components. My original assertion is that different products did indeed talk to each other. Back then IBM was king of the world (I made my money primarily working on IBM equipment) and everyone else was a minor player.
My point is that Apple chose to do that, and that decision has had consequences. IBM mainframe shops looking to adopt PCs back in the early 80's bought IBM PCs because they could get that integration right out of the box, supported by the same vendor end-to-end. Adopting MACs meant having to rely on a third party, and if it went sideways you potentially had three different vendors involved in solving it, one of which was openly hostile to your mainframe vendor.
IBM provided that solution in 1983, along with a single point of contact for support, and for many companies that made choosing that platform an intuitive decision. Once the decision was made to adopt the IBM/MS/Wintel solution the installed base soon represented an investment in money and internal support resources that set the stage for that becoming the development platform going forward.