Your comment is about business use of computers, not households. I worked at a Fortune 200 company and from 1985-1989 much of my job was helping roll out desktop computers and networking (including email) throughout our fairly large geographical territory. By 1990 I'd estimate conservatively that well over half of our office workers had their own networked PC on their desk.

I remember buying an AST 386 for my use at home, I'm guessing it cost about $4K or more in today's dollars, so it is true that business-class PCs at home were probably relatively rare at that time.