Correct, just like with the Commodore 64, the CPU clock actually differed based on the graphics hardware output, which was back in the day adjusted for the household CRT TV sets.

The master clock crystal oscillator on the motherboard was set to be 2 clock cycles per pixel and other chips clocks were derived from that.

Hence the CPU was set to 1/4th of master clock, so the European PAL[1] machines (a 50fps TV standard) actually ran slightly slower than the American NTSC[2] machines (a 60fps TV standard with a smaller vertical resolution).

[1] http://en.wikipedia.org/wiki/PAL

[2] http://en.wikipedia.org/wiki/NTSC