I'm sure you're right about overlap; I know that the Spectrum was probably the best-selling machine in the UK at the time, so there must be thousands of people who starting programming as a direct result of owning one.

There are whole scenes I'm utterly unaware of, like the Atari vs Amiga thing that I remember reading about at the time but paid no attention to. I'll pretend those users were more at home with the PC!