well, as byuu explained once, it's part of the way a real tv would diplay snes output: a tv would not be able to separately show the 512 pixels present in hires or pseudo hires mode (i.e. no alternate columns as in the first screen, but only a blended mix of the two as in the second one).
Err, perhaps not, but that would only be due to the dot pitch of the phosphor mask, not anything inherent to the NTSC signal carrying the video signal itself, yes?