In his famous commencement speech Steve Jobs took credit for bringing proportional spacing to the personal computer, claiming that Microsoft wouldn't have had the vision to do so. It's possible his claim was tongue-in-cheek, but Mr. Manjoo at Slate took it seriously in his appraisal of Jobs. " If he hadn’t brought proportional typefaces to the Mac—if the Mac had never existed—it’s difficult to think of anyone else who would have. Microsoft? Dell? No way."
I beg to differ. Several lines of development came together on the personal computer. IBM in 1948 announced the IBM Executive Typewriter, which provided a proportionally spaced font. To the best of my knowledge, such typewriters were always a class symbol, used for "executives". A second line was preparation of copy for photo-offset printing, with the Varityper and later the IBM Selectric Composer. A third line started with the mainframe with the creation of typesetting. These separate lines stemmed from the realization that print is just easier to read and prettier to look at if it's proportionally spaced, which then gets you into the details of font design, serifs versus no serifs, etc. etc. It didn't take Steve Jobs for people to realize this. He didn't create the demand for it from scratch.
My own exposure to the issue came in the early 70's, when we were using IBM mag tape/selectric typewriters for directives. We were looking for replacement systems, which got me looking far afield at the minicomputers of the day. The monitors on these were limited:; they could form letters with maybe a 6x9 dot matrix. And their output was limited to the dot matrix or daisy wheel printer.
Another way to discuss this is to focus on the final product, which is "what you see is what you get"--WYSIWYG, both on the monitor and on the output device. The Executive typewriter, Varityper, Composer all used hardware to provide the output. WYSIWYG on the monitor required getting enough pixels on the screen to model different type fonts. WYSIWYG on the output device required a device which could vary the output under software control: inkjet, dot-matrix, or laser printers. And, of course, you needed a software package between the monitor and output device.
What Apple did do by the mid-80's was package the three elements (monitor, software, laser printer) together in a package which could enable desktop publishing. Once that was in place the doors opened wide and demand rushed in.