I think for the time period, hobbyists can't be written off either. My dad got into Commodore and Atari in the late 70's/early 80's, and sparked my interest in software. Computing already wasn't cheap, but if the home consumer needed to pay for extra licensing fees, I could easily see adoption being far more limited to business. I think a lot of developers, myself included, got their start as hobbyists and never would have caught the "itch" to develop if for not this early exposure at home.