The maximum resolutions are:
PAL is 720x576 @50Hz interlaced.
NTSC is 720x480 @60Hz interlaced.
These both have the same bandwidth i.e. (720x576x50 = 720x480x60)
Same goes for non-interlaced...
PAL is 720x288@50
NTSC is 720x240@60
Same bandwidth i.e. 720x288x50 = 720x240x60
I thought there might be a relationship between the Amiga resolutions
640x256@50 /= 640x200@60
BUT it is close and they are nice round number
I honestly dont know.
BUT THERE IS AN ANSWER... Why?
Because the Atari ST uses the same resolutions so it's not hardware specific.