Well the internal framebuffers for those consoles might not be in a common aspect ratio but since they are made to be displayed on 4:3 TVs they don't qualify.
We don't really want to enumerate aspect ratios that are not allowed. Generally speaking you either make something that's square, longer than widescreen or in a tall format such as in arcade cabinets. The idea is to make something where it is clear it's not a standard resolution so making something in say 4:3.2 would defeat that purpose ;)