Indeed. By far the largest majority of home micros in the 1970s to early 1980s fell into one of those three camps: 8080/Z80, 6502, or 6800-series.
There were other CPUS around, but used much less commonly. I remember buying a book (must have been about 1979 or 1980) on the Texas Instruments 9900 (number?) CPU.
It was so different at the time to the other main chips in use. 16-bits for a start, and instead of dedicated accumulators, index registers and so on it just had a whole bunch of general-purpose registers which you could use for any purpose.
But those old 8-bit CPUs can still be very useful in controller applications. The Z80 survived for many more years as a dedicated controller for disk drivers, terminals, printers, etc. before the newer generation chips started to take over. My library still contains a whole range of books on machine-code programming for 6502/Z80/6800 chips.
