Usually, computers that came in separate PAL and NTSC versions used slightly different CPU frequencies because the video and CPU clock were derived from the same crystal (the Apple II and Commodore 64 were already mentioned here, and this excellent answer goes into the history of color computers).
However, the Amiga could be switched in software between PAL and NTSC by holding both mouse buttons on power up. This seems to be an addition made for the ECS chipset over the OCS chipset.
That makes me wonder: Was the Amiga capable of running the CPU at two different speeds (Wouldn't that require two different crystals, one for PAL and one for NTSC?), or was the ECS chipset capable of generating it's own clock signal, thus finally making the video clock completely independent of the CPU clock?