it was the marketing strategy of mac back in the 80s
they needed to twist the minds of the consumers, make them think the world was changing and they reinvented the computer or something.
personal computer was obviously a term that defined any computers in a household, as was revolutionary.
well mac didnt want to be put in the same boat. apple needed you to think they were above that "old" industry of that time.
well obviously it wasnt always mac/pc, then it was apple/pc. same thing