theprestige
Penultimate Amazing
Unfortunately, PC has become synonymous with "a computer running Microsoft Windows", probably because of the incredibly stupid "I'm a PC" "I'm a Mac" adverts.
I think it's the other way around. "PC" and "Mac" were chosen for those ads because the marketing team knew they were already in common use and would properly convey the distinction they were selling.
I'm pretty sure the terms and the distinction were around since at least the mid-90s.
I'm also pretty sure there's nothing "unfortunate" about this development. Languages evolve all the time, especially during the creation of a new family of context-specific terms like jargon for a new technical field. And there's not actually any rule of language mandating that compound words and derived words must be a literal conjunction of the component or source words.
There's nothing insightful or productive about resisting the usage of "PC" to mean "personal computer running some form of OS other than Apple's Mac OS family".